Add ffsl(), ffsll(), fls(), flsl(), flsll() and use GCC's __builtin_ctz/__builtin_clz for faster implementation of these

I needed to use DS3231, I remember that in past it worked ok, but now for stm32f4xx is used another driver (chip specific, stm32f40xxx_i2c.c) and DS3231 driver doesn't work. After investigating a problem I found that I2C driver (isr routine) has a few places there it sends stop bit even if not all messages are managed. So, e.g., removing stm32_i2c_sendstop (#1744) and adding stm32_i2c_sendstart after data reading helps to make DS3231 working.  Verified by David Sidrane.

The interrupt occurs over the counter overflow

Approved-by: Gregory Nutt <gnutt@nuttx.org>

fix compile error when disabled the flash data cache corruption for stm32 f1xx

Approved-by: Gregory Nutt <gnutt@nuttx.org>

stm322_flash:missing unlock on F1 HSI off path

Approved-by: Gregory Nutt <gnutt@nuttx.org>

stm32_i2c_alt:Move def of regval to top func def per CS

Approved-by: Gregory Nutt <gnutt@nuttx.org>

Upstream stm32 build fixes

Approved-by: Gregory Nutt <gnutt@nuttx.org>

Merged in david_s5/nuttx-14/david_s5/stm32f7stm32_allocateheapc-there-are-5-c-1490226997884 (pull request #290)

stm32f7:stm32_allocateheap.c There are 5 configurations

Approved-by: Gregory Nutt <gnutt@nuttx.org>

STM32 Flash fixes

Approved-by: Gregory Nutt <gnutt@nuttx.org>

This is a know hardware issue on some STM32 see the errata of your model
and if you make use of both memory banks you should enable it.

Writing to a flash sector while starting the erase of other sector
have a undefined behavior so lets add a semaphore and syncronize
access to Flash registers.

But for the semaphore to work it needs to be initialized so each
board needs call stm32_flash_initialize() on initialization, so
to avoid runtime problems it is only using semaphore and making
it thread safe if initialized, after all boards starts to call
stm32_flash_initialize() we can remove the boolean and the check.

Erase a sector from the second bank cause the bit 4 of SNB being set
but never unsed, so trying to erase a sector from the first bank
was acually eraseing a sector from the second bank.