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

For some platforms, after turning on the VREG for ADV7533 bridge
chip, need to sleep some period of time before doing any
I2C transactions with the bridge chip.

Change-Id: I6f7c45f3561f996507613a7a6eb0bcd8922caed5
Signed-off-by: Yunyun Cao <yunyunc@codeaurora.org>