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: I5a325e40bde1bead831da95c0a3c7be8fc9c5c00
Signed-off-by: kamasali Satyanarayan <quic_kamasali@quicinc.com>
(cherry picked from commit 3e7d8562a1)