msm_fb: display: protect dma status for video mode panel

There is a possibility of race condition between dma update in ioctl
context and isr context, hence  add spinlock to protect the dma status
in video mode type panel for safety in dual core environment.

Change-Id: I85a2d76d62816ad92a7b0d60f7788f6c551f8dfb
Signed-off-by: Jeevan Shriram <jshriram@codeaurora.org>