ARM: dts: msm: Add pcie-ep device for msm8996

With the pcie-ep device, pcie0 can work in endpoint mode.
But it's disabled by default for the function conflict with
pcie0 in host mode.

Change-Id: Ia39edf8dd8fc2a1b3ed79db13aa6f85065ebf7b0
Signed-off-by: Yimin Peng <yiminp@codeaurora.org>