This function may be called from a UART IRQ, which may interrupt the system
when it is erasing/reading/writing flash. In such a case all code
executing from the IRQ must be in iRAM (because the SPI flash is busy), so
put mp_keyboard_interrupt in iRAM so ctrl-C can be caught during flash
access.
This patch also takes get_fattime out of iRAM and puts it in iROM to make
space for mp_keyboard_interrupt. There's no real need to have get_fattime
in iRAM because it calls other functions in iROM.
Fixes issue #3897.
d800ed1877