msm: mdss: fix iommu issue in recovery mode for 8909

Since dsi 6G uses iommu calling blank while continuous
splash is on will lead to iommu faults. In general  dma
is stopped after sending panel off commands. Stop the
dma before sending off commands if continuous splash is
still on as iommu attach by dsi will result in faults
in dma. Also update the continuous splash flag correctly
in this case.

Change-Id: I67f8d5a2b8f73525dba3b354bffc0145bfb7beb1
Signed-off-by: Shivaraj Shetty <shivaraj@codeaurora.org>