drm/msm/gem: Move prototypes

These belong more cleanly in the gem header.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20220411215849.297838-2-robdclark@gmail.com


Signed-off-by: Rob Clark <robdclark@chromium.org>