Commit c046b23ea29e0183c899a8dbe1da3bed3440a255 prevented frozen boot code
from being interrupted by Ctrl-C, but that means a corrupt filesystem will
forever lock up an esp32/esp8266 board. This commit fixes that by
explicitly enabling Ctrl-C before running the forever loop.
Signed-off-by: Damien George <damien@micropython.org>