boards: cc1352p1_launchxl: new board, support antenna switching

Added new CC1352P1 LaunchXL board supporting 20dBm TX for its
sub-GHz radio.

Note that the board has a multiplexer circuit to switch between
2.4GHz, High-Power TX and Sub1GHz states, for which a custom board
module was implemented, together with board-specific device-tree
bindings and pinctrl definitions for each of the RF states.

Signed-off-by: Stancu Florin <niflostancu@gmail.com>