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.