drm/msm: add mdss_smmu_request_mappings definition for non-FB targets

SDE rotator uses V4L2 target. Currently mdss_smmu_request_mappings
is defined only within the FB driver. For targets not using FB
this shall cause compilation issue.

Add definition of mdss_smmu_request_mappings for DRM based devices.

Change-Id: I26ef267802845236193b4c2688712e37a178e6cb
Signed-off-by: Abhinav Kumar <abhinavk@codeaurora.org>