drm: remove unused drm_gem.h include

There's nothing GEM related in the file - the drm_gem.h include is not
needed.

Signed-off-by: Emil Velikov <[e-mail]>
Acked-by: Sam Ravnborg <[e-mail]>
Reviewed-by: Thomas Zimmermann <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/drm_vm.c

···
 #include <drm/drm_drv.h>
 #include <drm/drm_file.h>
 #include <drm/drm_framebuffer.h>
-#include <drm/drm_gem.h>
 #include <drm/drm_print.h>
 
 #include "drm_internal.h"