drm/etnaviv: clean up includes

Drop unused includes, move more includes from the generic etnaviv_drv.h to
the units where they are actually used, sort includes.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Acked-by: Sam Ravnborg <sam@ravnborg.org>

drivers/gpu/drm/etnaviv/etnaviv_gem.c

@@ -5,8 +5,6 @@
 
 #include <drm/drm_prime.h>
 #include <linux/dma-mapping.h>
-#include <linux/sched/mm.h>
-#include <linux/sched/task.h>
 #include <linux/shmem_fs.h>
 #include <linux/spinlock.h>
 #include <linux/vmalloc.h>