msm_fb: display: add mfd null pointer and mfd panel_power_on checks

These checks are necessary for the situations where display is off but
vsync ctrl enable or disable is still called.

CRs-Fixed: 462586
Change-Id: I2ee43ff323da38359f3bff28669df19b87d8343d
Signed-off-by: Huaibin Yang <huaibiny@codeaurora.org>
msm_fb: display: fix the hang issue caused by solidfill pipe

When mdp pipe solidfill mode is disabled, the staled pipe info is used
to update mdp pipe regs. This caused mdp hang. Since
mdp4_overlay_rgb_setup function already resets solidfill mode, this
patch removes any pipe register updates that are related to disabling
solidfill mode.

CRs-fixed: 467555
Change-Id: I23f4b29731c9097ab0cc38baa00cd35bc536d2ba
Signed-off-by: Huaibin Yang <huaibiny@codeaurora.org>