msm: pcie: add support to manage PCIe PHY PLL block

Some chipsets require PCIe root complex driver to manually
control PCIe PHY PLL block. Add support to power on PCIe PHY PLL
block if it has been manually powered down.

Change-Id: Iee2b7e9fd80e537a0b2983827261297c8642a3b7
Signed-off-by: Tony Truong <truong@codeaurora.org>