ARM: dts: msm: Update PCIe EP link speed for sdxprairie

On resume from hibernate/sleep the PCIe EP link is re-configured
and enabled. Update the link speed to Gen3 speed.

Change-Id: Ia31d3bdfaa9785eb035debf458547e4454e3c37f
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>