Add boot_config reg reading support for shdci bootdevice
node through nvmem cell to check if the boot device is
emmc or ufs.
Change-Id: I341de8e37df9c2758889abf7c643b8a66c82f9d9
Signed-off-by: kamasali Satyanarayan <quic_kamasali@quicinc.com>
(cherry picked from commit 0c56d694fc)