MLK-10058-3 arm: gpc: add pcie phy power gpc operations

For PCIe module on i.mx6sx, some GPC operations would
be mandatory required when PCIe PHY is powered on/off.
So we need update gpc driver for the new requirements.
We implement it by regulator notify framwork in gpc driver.
NOTE:
make sure gpc driver is ready before PCIe driver is probed.
Otherwise, cause system hang during PCIe driver probe,
because the notify NOT installed ready and the gpc will
NOT power on PCIe.

Signed-off-by: Richard Zhu <Richard.Zhu@freescale.com>