MLK-10591-2 ARM: imx: add necessary delay for gpc power switch

MLK-10591-2 ARM: imx: add necessary delay for gpc power switch

Per design team's requirement, when GPC switch power req is
assert and self-clear, need to add delay to make sure power
switch is actually up, the delay value can be got from below:

delay = 2us * 66MHz / IPG_RATE,

here we add 2us margin to make it more reliable, currently only
display mix and pu mix are a power switch.

Signed-off-by: Anson Huang <b20788@freescale.com>
Signed-off-by: Robin Gong <b38343@freescale.com>
(cherry picked from commit 39601d70efcf49a91da01be7dff6e8c0d4b061ad)