fb: msm_dba: add post-on-sleep support for adv7533 vreg

For some platform, after turning on the VREG for ADV7533 bridge
chip, it needs to sleep some period of time before doing any
I2C command with the bridge chip. This value is configurable
through DTS node.

Change-Id: Ia7d1009a91c3ed6a3eff182ade553cb3d8e2e35d
Signed-off-by: Jin Li <jinl@codeaurora.org>