[DISCO_F429ZI] changed clock settings

Original STM32Cube F4 driver sets SYSCLK for STM32F429 to 16MHz. This
adds a 168MHz and 180MHz configuration to system_stm32f4xx.c generated
by STM32CubeMX code generator. The rtos clock configuration is changed
too. In singletest.py run everything is OK.
IAR: Fixed language settings in ewp files. Set project setting to allow both c and c++ language and allowed VLA in C code
updating app_timer.c from Norid'c SDKv7.1.0; hoping to fix the hangs reported around timers
[DISCO_F429ZI] changed clock settings

Correction of wrong comments.
Merge pull request #797 from ohagendorf/DISCO_F429_clockcycle

Targets: DISCO_F429ZI - clock frequency additions
Merge pull request #796 from GustavWi/iar_mbed

IAR: Fixed language setting in ewp files (VLA enable)
Merge pull request #798 from rgrover/master

Targets: nrf51 - updating app_timer.c from Norid'c SDKv7.1.0