drm/cirrus: Use VGA macro constants to unblank

Set the VGA bit for unblanking with macro constants instead of magic
values. No functional changes.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230215161517.5113-18-tzimmermann@suse.de

drivers/gpu/drm/tiny/cirrus.c

@@ -509,7 +509,7 @@ static void cirrus_crtc_helper_atomic_enable(struct drm_crtc *crtc,
 	cirrus_mode_set(cirrus, &crtc_state->mode);
 
 	/* Unblank (needed on S3 resume, vgabios doesn't do it then) */
-	outb(0x20, 0x3c0);
+	outb(VGA_AR_ENABLE_DISPLAY, VGA_ATT_W);
 
 	drm_dev_exit(idx);
 }