driver: ieee802154: rf2xx: implement setting tx power
driver: ieee802154: rf2xx: implement setting tx power

Implemented rf2xx_set_txpower() in ieee802154_rf2xx.c by mapping dBm
values to RF2XX register values.

Signed-off-by: Kari Severinkangas <e58a6e7a650c1164f28136136a7f5cc57bae6dcc@tridonic.com>
Signed-off-by: Markus Becker <41b3d55dd769bc12df1d891e8cfd1d03607af5b4@tridonic.com>

finikorg/zephyr,finikorg/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr,nashif/zephyr,galak/zephyr,galak/zephyr,Vudentz/zephyr,Vudentz/zephyr,nashif/zephyr,nashif/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,Vudentz/zephyr