drm: msm: read SDE registers for splash case

Read sde registers like layer mixer and ctrl information
from bootloader when early splash is enabled in bootloader.
These information will be updated to kernel resource
manager to let bootloader and kernel use the same hardware
setting.

CRs-Fixed: 2225630
Change-Id: I0e971de1992b380e30933f476b1a7e185ce0ad96
Signed-off-by: Guchun Chen <guchunc@codeaurora.org>
Signed-off-by: Camus Wong <camusw@codeaurora.org>