It is enabled by default to get the standard behaviour of doing a reset
after it is finished, but can be disabled by a board to jump straight to
the application (likely the board needs to use MBOOT_BOARD_CLEANUP to make
this work).
The application is passed a reset mode of BOARDCTRL_RESET_MODE_BOOTLOADER
if the bootloader was active and entered via a jump.
Signed-off-by: Damien George <damien@micropython.org>