Add initial support for Blue Pill Plus board
This add support of Blue Pill Plus STM32F103CBT6 with a new configure option:
--target=BLUE_PILL_PLUS
This is following the merge of:
Thus, it requires f3eb84c3e9bfdb0a700f67f2b9313d730dbd7009 commit in chopstx.
Signed-off-by: Alexandre Esse alexandre.esse.dev@gmail.com