drm/msm: expose msm framebuffer init for SDE layer

This change exposes the previously static msm_framebuffer_init
function so that it can be utilized in the SDE DRM driver code.

Change-Id: I4c27d819929deda9671046c583e29a7ba0c07c3f
Signed-off-by: Steve Cohen <cohens@codeaurora.org>