STM32 OTG HS:  A little research reveals that only the F2 RCC initialization set the OTGHSULPIEN bit and Photon is the only F2 board configuration that uses OTG .  Therefore, we can simplify the conditional logic of the last PR.  Negative logic was used (#ifndef BOARD_DISABLE_USBOTG_HSULPI) to prevent bad settings in other configurations.  But give these facts, the preferred positive logic now makes more sense (#ifdef BOARD_ENABLE_USBOTG_HSULPI).

STM32: Review of last STM32 F2 PR.  Progate changes to STM32 F4 and F7 OTGHS.  Rename some configs/photon/src files.  Naming can be either photon_ or stm32_ but must be consistent.

stm32f20xxx: add BOARD_DISABLE_USBOTG_HSULPI flag

Approved-by: Gregory Nutt

Merged in david_s5/nuttx-13/david_s5/as-discovered-by-dcabecinhas-this-fix-as-1489246417893 (pull request #264)

As discovered by dcabecinhas. This fix assume the 8 byte alignment options for size stack size or this will overwrite the first word after TOS

Approved-by: Gregory Nutt

As discovered by dcabecinhas. This fix assume the 8 byte alignment options for size stack size or this will overwrite the first word after TOS
See https://github.com/PX4/Firmware/issues/6613#issuecomment-285869778

photon: add usb otg hs support and usbnsh app

Approved-by: Gregory Nutt

photon: add iwdg timer support

Approved-by: Gregory Nutt

STM32 F33 ADC: Correct bad definitions of base addresses; Fix naming collision by changing colliding STM32_ADC12_BASE to STM32_ADC12_CMN_BASE

drivers/wireless/nrf24l01.c:  Review last PR.  Also got enthused and did major re-work to file to bring it closer to the NuttX coding style.  Fixed a few compile time warnings.

multiple fixes in nrf24l01 driver

Approved-by: Gregory Nutt

- signal POLLIN if there is already data in the FIFO
- send ETIMEDOUT to userspace after 2 seconds if TX IRQ was not received
- handle FIFO overflow
- handle invalid pipes/empty FIFO
- multiple cosmetics (missing static, duplicate define, missing \n)

configs: add Particle Photon board support

Approved-by: Gregory Nutt

Priority Inversion fixes

Approved-by: Gregory Nutt

All STM32 host drivers.  In IN endpoint retry, delay for a clock tick to give some breathing space for the CPU.  EXPERIMENTAL change.

STM32, STM32 F7, and STM32 L4: Clone Freddie Chopin's I2C change to similar STM32 I2C drivers.

Approved-by: Gregory Nutt

Priority inheritance:  When CONFIG_SEM_PREALLOCHOLDERS==0, there is only a single, hard-allocated holder structure.  This is problem because in sem_wait() the holder is released, but needs to remain in the holder container until sem_restorebaseprio() is called.  The call to sem_restorebaseprio() must be one of the last things the sem_wait() does because it can cause the task to be suspended. If in sem_wait(), a new task gets the semaphore count then it will fail to allocate the holder and will not participate in priority inheritance.  This fix is to add two hard-allocated holders in the sem_t structure:  One of the old holder and one for the new holder.

pthreads:  Fix pthread_mutexattr_init().  It was not initializing the protocol field when priority inheritance is enabled.

   Save elapsed time before handling I2C in stm32_i2c_sem_waitstop()
   This patch follows the same logic as in previous fix to
   stm32_i2c_sem_waitdone().
   It is possible that a context switch occurs after I2C registers are read
   but before elapsed time is saved in stm32_i2c_sem_waitstop(). It is then
   possible that the registers were read only once with "elapsed time"
   equal 0. When scheduler resumes this thread it is quite possible that
   now "elapsed time" will be well above timeout threshold. In that case
   the function returns and reports a timeout, even though the registers
   were not read "recently".
   Fix this by inverting the order of operations in the loop - save elapsed
   time before reading registers. This way a context switch anywhere in the
   loop will not cause an erroneous "timeout" error.