ARM: dts: msm: Early mount of vendor partition for SDM845

Add support to early mount vendor partition from device tree. This is
required so that vendor modules can be loaded during early-init.

Change-Id: Ic0864cc793eda12a40399225049d8eb5ea4a6019
Signed-off-by: Puja Gupta <pujag@codeaurora.org>