msm: mdss: fix dsi buf_aloc when using physical memory

Set the dmap to correct translated physical address during
dsi_alloc_buf and also include GPF_DMA flag during kzalloc
to ensure the address allocated is 32-bit.

Change-Id: I5b0445eda6c4a93ca321ca9469626ecce4a167e9
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>