Revert "ARM: dts: msm: disable reg dma block for sdm845"

Reg dma last command sequence was stalling the sde pipeline. Issue has
been fixed now, re-enabling the reg dma block.

This reverts commit 608099ba.

Change-Id: Ia71e83a991e80e9934e46e651e4fad9a0750acb4
Signed-off-by: Gopikrishnaiah Anandan <agopik@codeaurora.org>