msm: sde: fix mem access of sde rotator regdma ram

regdma ram of sde rotator is mapped as device io, so any write access to
it should be using writel interface. A direct u32 pointer manipulation
will easily cause access page fault due to compiler optimization. This
fix includes the following:
- add proper __iomem attribute to allow sparse checking
- using writel_releaxed_no_log macro for all write access to the regdma
  ram
- maintain 32bit alignment for any regdma write pointer update

Change-Id: Idbb0681d501b4d960fddc80ac821c5564265ffc2
Signed-off-by: Benjamin Chan <bkchan@codeaurora.org>