target: msm8996: add intermediate splash status to kernel

Once kernel sends stop splash signal to bootloader, bootloader
needs to write one intermediate status to kernel to notify it
has finished last frame update and kernel can continue its own
process, otherwise, one race condition about mixer setup and
clear may happen.

Change-Id: I16e2930c0da8830fc8f066291f0172cad1a4b973
Signed-off-by: Guchun Chen <guchunc@codeaurora.org>