[SYSDATA] Added var 'sysdatadevice' and writing enabling on 'mmcblk0boot1'

Due to Mediatek architecture is necessary to handle the new partition mmcblk0boot1 in the RAUC/Sysdata process. Has been introduced the new var sysdatadevice in bootargs, which is sysdata_device in previous SOC, while is sysdata_device+"boot1" in Mediatek architecture. This var will be used in sysdata scripts. No functional changes are introduced for RK and IMX. Mediatek needs also to unlock writing on mmcblk0boot1 before making changes through RAUC/Sysdata; we abilitate with file /sys/block/mmcblk0boot1/force_ro