msm: pcie: update RC MPS based on MPSS

Scale PCIe RC Max Payload Size (MPS) based on its capability
Max Payload Size Supported (MPSS). Configurating RC MPS to the
largest setting possible will help improve overall PCIe link
bandwidth performance.

Change-Id: Ice31cf0ab97fd7dd83736eea77e42ff00fb3148c
Signed-off-by: Tony Truong <truong@codeaurora.org>