Allows to enter one of the u-boot's recovery options (ums, rockusb, fastboot) or maskrom with recovery button.
Entering one of the options is done by holding the recovery butting during boot:
one flash (2s) - switch board to ums mode
two flashes (+2s) - switch board to rockusb mode
three flashes (+2s) - switch board to fastboot mode
four flashes (+2s) - switch board into maskrom mode
Enabled on RockPro64 initially (ums, rockusb and maskrom).
It will spread to other boards that have the button.