dts: nrf: Add flash controller and alignment description for nRF51822
dts: nrf: Add flash controller and alignment description for nRF51822

Similar addition was don previous for nRF52840.
Added flash-controller description and moved flash description to
it. Added property for description of
the flash alignment required by write operations.


Signed-off-by: Andrzej Puzdrowski <0222c24e1773dd88269ed0e559909ec9bea3604a@nordicsemi.no>

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