ARM: dts: msm: add PCIe endpoint node for sm8150/sa8155

Add PCIe endpoint node to device tree of sm8150/sa8155. PCIe core
is in endpoint mode and communicates with the PCIe root complex
on host side.

Change-Id: I229eee80e3a7d2c32ca50b4b4a7212ef1be003cd
Signed-off-by: Tony Truong <truong@codeaurora.org>
Signed-off-by: Rama Krishna Phani A <rphani@codeaurora.org>