[ALPS08848700] drm: dsi: Support dynamic fps by sendng CMD in VFP

[Description]
Some panel need send command in VFP when switch fps.
Add code flow to support this feature

[Test]
Test ok

MTK-Commit-Id: 4ad53138820a8e06c8c58e076999118e474b3c71

Signed-off-by: Huijuan Xie <huijuan.xie@mediatek.com>
CR-Id: ALPS08848700
Feature: Always On Display
Change-Id: I243e4b8a5d78e13ef30ec8643df00fbe6d82ca33