arm/dt: 8974-v2: declare HDMI Tx differences from 8974 v1 to v2

Register address space for HDMI Tx has increased between 8974 v1 and v2.
Handle it by overriding default register mapping from mdss device tree.

Change-Id: I16720a74145654fd6b78d159055f8dc2965b5094
Signed-off-by: Ujwal Patel <ujwalp@codeaurora.org>