stm32/mboot: Fix mp_hal_delay_us() and add mp_hal_ticks_ms().
stm32/mboot: Fix mp_hal_delay_us() and add mp_hal_ticks_ms().

Signed-off-by: Damien George <99e6b749acbfbe2a596df99e91d24d6e1fdbee00@micropython.org>

pfalcon/micropython,pfalcon/micropython,pfalcon/micropython,pfalcon/micropython,pfalcon/micropython