Bluetooth: controller: Disable PA/LNA for nRF51x
Bluetooth: controller: Disable PA/LNA for nRF51x

The PA/LNA feature is not functional on nRF51x series due to added
interrupt latency. Disable this feature unconditionally for those ICs to
avoid unexpected behavior.

Signed-off-by: Carles Cufi <853081dc8dca4fe6a7e3c984752718b5db36e060@nordicsemi.no>

ldts/zephyr,zephyriot/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,ldts/zephyr,aceofall/zephyr-iotos,ldts/zephyr,explora26/zephyr,fbsder/zephyr,punitvara/zephyr,ldts/zephyr,explora26/zephyr,punitvara/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,nashif/zephyr,Vudentz/zephyr,fbsder/zephyr,GiulianoFranchetto/zephyr,punitvara/zephyr,explora26/zephyr,nashif/zephyr,nashif/zephyr,fbsder/zephyr,explora26/zephyr,Vudentz/zephyr,aceofall/zephyr-iotos,GiulianoFranchetto/zephyr,Vudentz/zephyr,mbolivar/zephyr,kraj/zephyr,fbsder/zephyr,finikorg/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,zephyriot/zephyr,zephyrproject-rtos/zephyr,aceofall/zephyr-iotos,zephyrproject-rtos/zephyr,fbsder/zephyr,mbolivar/zephyr,aceofall/zephyr-iotos,aceofall/zephyr-iotos,GiulianoFranchetto/zephyr,mbolivar/zephyr,Vudentz/zephyr,zephyriot/zephyr,galak/zephyr,mbolivar/zephyr,galak/zephyr,kraj/zephyr,finikorg/zephyr,kraj/zephyr,kraj/zephyr,kraj/zephyr,zephyriot/zephyr,nashif/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,zephyriot/zephyr,finikorg/zephyr,finikorg/zephyr,Vudentz/zephyr,Vudentz/zephyr,punitvara/zephyr,punitvara/zephyr,ldts/zephyr,galak/zephyr,galak/zephyr,explora26/zephyr,mbolivar/zephyr