stm32f4: fix incorrect baud rate calculation for USART2

USART1 and USART6 are on APB2 whose frequency is 84MHz,
while USART2, USART3, UART4, and UART5 are on APB1 whose
frequency is 42
MHz (max).

Commented-by: Shih-Po Hung <arcbbb@gmail.com>
Signed-off-by: Jim Huang <jserv@0xlab.org>
bump copyright date for banner
revise the license terms
README: update verified toolchain list
improve the descriptions about external sources
start: replace init_*_seg with memset/memcpy
Merge pull request #95 from rampant1018/master

start: replace init_*_seg with memset/memcpy
entry: replace init_*_seg with memcpy/memset
Merge pull request #96 from rampant1018/master

loader: replace init_*_seg with memcpy/memset
platform: add stm32-common to place stm32 specific code
platform: Move shareable gpio functions to stm32-common
platform: Move shareable rcc functions to stm32-common
platform: Move shareable mpu functions to stm32-common
platform: Move shareable nvic functions to stm32-common
platform: Move shareable systick function to stm32-common
platform: Move shareable hwtimer functions to stm32-common
platform: Move shareable usart functions to stm32-common
config: add platform selection in Kconfig
platform: Add stm32f429i platform support
mempool: Add AHB1 memory pool declaration