boards: cc1352r1_launchxl / cc26x2r1_launchxl: enable ROM bootloader

This enables the ROM bootloader on the CC13x2 / CC26x2 LaunchPad
development boards. The bootloader can be started by holding BTN-1
during reset. This can be useful during development to recover a board
if DAPs get disabled.

Signed-off-by: Brett Witherspoon <spoonb@cdspooner.com>