drm/msm/sde: add parsing logic for sec_sid_mask

Get the secure SID mask from device tree, so it can
be configured based on the target. The mask is used
during secure-camera/secure-display switch scm_call

Change-Id: Icdf35cb23287921f53d8f0fe01fe26133bf454e4
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>