drm: msm: improve early splash mechanism

Early RVC will keep running even if all display's splash
in bootloader are stopped. So kernel splash handoff
mechanism needs to be modified to match the scenario.

CRs-Fixed: 2225630
Change-Id: I0e00403f6cae0401ea23465f78cf092abfa2a611
Signed-off-by: Guchun Chen <guchunc@codeaurora.org>