configs/clicker2-stm32:  Cleans up minor issues

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

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>