drm/vmwgfx/vmwgfx_kms: Mark vmw_{cursor,primary}_plane_formats as __maybe_unused

Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/vmwgfx/vmwgfx_kms.h:256:23: warning: ‘vmw_cursor_plane_formats’ defined but not used [-Wunused-const-variable=]
 drivers/gpu/drm/vmwgfx/vmwgfx_kms.h:248:23: warning: ‘vmw_primary_plane_formats’ defined but not used [-Wunused-const-variable=]
 drivers/gpu/drm/vmwgfx/vmwgfx_kms.h:256:23: warning: ‘vmw_cursor_plane_formats’ defined but not used [-Wunused-const-variable=]
 drivers/gpu/drm/vmwgfx/vmwgfx_kms.h:248:23: warning: ‘vmw_primary_plane_formats’ defined but not used [-Wunused-const-variable=]
 drivers/gpu/drm/vmwgfx/vmwgfx_kms.h:256:23: warning: ‘vmw_cursor_plane_formats’ defined but not used [-Wunused-const-variable=]
 drivers/gpu/drm/vmwgfx/vmwgfx_kms.h:248:23: warning: ‘vmw_primary_plane_formats’ defined but not used [-Wunused-const-variable=]

Cc: VMware Graphics <linux-graphics-maintainer@vmware.com>
Cc: Roland Scheidegger <sroland@vmware.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Zack Rusin <zackr@vmware.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210115181313.3431493-8-lee.jones@linaro.org

drivers/gpu/drm/vmwgfx/vmwgfx_kms.h

@@ -245,7 +245,7 @@ struct vmw_framebuffer_bo {
 };
 
 
-static const uint32_t vmw_primary_plane_formats[] = {
+static const uint32_t __maybe_unused vmw_primary_plane_formats[] = {
 	DRM_FORMAT_XRGB1555,
 	DRM_FORMAT_RGB565,
 	DRM_FORMAT_RGB888,
@@ -253,7 +253,7 @@ static const uint32_t vmw_primary_plane_formats[] = {
 	DRM_FORMAT_ARGB8888,
 };
 
-static const uint32_t vmw_cursor_plane_formats[] = {
+static const uint32_t __maybe_unused vmw_cursor_plane_formats[] = {
 	DRM_FORMAT_ARGB8888,
 };