ARM: dts: msm: Add sdhc2 for sdm670 rumi

Add sdhc2 for enabling SD card on sdm670 rumi target. This will
enable the kernel to register and use SD card in rumi. Currently
bus bandwidth voting and speeds higher than 50Mhz are not supported
in the RUMI. Also since card detect gpio is not yet assigned, the sd
card driver will do periodic polling instead.

Change-Id: I110257c76aa5dc6efb4a4fa204d3acd11dcd5fe9
Signed-off-by: Vijay Viswanath <vviswana@codeaurora.org>