ARM: dts: msm: Add the CX MISC GPU block on sdm845 and SDM670

The CX MISC GPU register block is used for a few configuration
settings. Add this block in the devicetree files for the targets
that have this block.

Change-Id: I064927bf44af78ea917d078cb6d7aba10cf0f057
Signed-off-by: Lynus Vaz <lvaz@codeaurora.org>