ARM: dts: msm: Add PCIe switch ASM2806 support for rb5

ASM2806 is a PCIe package switch under the PCIe0 in rb5 board.
And one of the down port is connected with QCA6390 SIP module.
Adding the dts setting to make QCA6390 is working fine.

Change-Id: I902baeddbbd4e83448c2af49734a7018f7aa4635