msm: pcie: slow down PCIe PHY RX clock for SVS mode

In order for PCIe to reliabily work in SVS mode,
the PCIe PHY RX clock needs to be slowed.

Change-Id: Ic6edf487011ef4ac71d486210b1f6176e2142551
Signed-off-by: Tony Truong <truong@codeaurora.org>