msm: kgsl: Disable VPC all flat shading optimization for A5XX

Set ALLFLATOPTDIS bit in A5XX_VPC_DBG_ECO_CNTL register to
disable VPC all flat shading optimization. ALLFLATOPTDIS is
a hardware chicken bit value needs to be set one, to avoid
UI rendering corruption.

Change-Id: I39b5ad098daacbb1c3b0fc93963d82d477f70cc1
Signed-off-by: Hareesh Gundu <hareeshg@codeaurora.org>