drm: vmwgfx: Replace drm_fb_get_bpp_depth() with drm_format_info()

The driver is the last users of the drm_fb_get_bpp_depth() function. It
should ideally be converted to use struct drm_mode_fb_cmd2 instead of
the legacy struct drm_mode_fb_cmd internally, but that will require
broad changes across the code base. As a first step, replace
drm_fb_get_bpp_depth() with drm_format_info() in order to stop exporting
the function to drivers.

The new DRM_ERROR() message comes from the vmw_create_dmabuf_proxy(),
vmw_kms_new_framebuffer_surface() and vmw_kms_new_framebuffer_dmabuf()
functions that currently print an error if the pixel format is
unsupported.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Sinclair Yeh <syeh@vmware.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1476744081-24485-12-git-send-email-laurent.pinchart@ideasonboard.com