This commit simplifies and cleans up the bare-arm port, and adds just
enough system and library code to make it execute on an STM32F405 MCU.
The mpconfigport.h configuration is simplified to just specify those
configuration values that are different from the defaults. And the
addition of -fdata-sections and -ffunction-sections means the final
firmware is smaller than it previously was, by about 4200 bytes.
A README is also added.
Signed-off-by: Damien George <damien@micropython.org>
Damien George