drm/sun4i: hdmi: Add missing drm_atomic header

Commit 358e76fd ("drm/sun4i: hdmi: Consolidate atomic_check and
mode_valid") added a call to drm_atomic_get_new_connector_state() but
didn't include drm_atomic.h which defines it.

On some configuration, this leads to a build failure, presumably because
in the common case the header gets included by an intermediate header
but it isn't always the case.

Let's add a proper include.
Reported-by: Dave Airlie <airlied@redhat.com>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202402291942.zVb1Vx4Y-lkp@intel.com/
Fixes: 358e76fd ("drm/sun4i: hdmi: Consolidate atomic_check and mode_valid")
Signed-off-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240301080249.823067-1-mripard@kernel.org

drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c

@@ -16,6 +16,7 @@
 #include <linux/regmap.h>
 #include <linux/reset.h>
 
+#include <drm/drm_atomic.h>
 #include <drm/drm_atomic_helper.h>
 #include <drm/drm_edid.h>
 #include <drm/drm_encoder.h>