drm/tilcdc: Add DRM_TILCDC_SLAVE_COMPAT for ti,tilcdc,slave binding support

Adds a CONFIG_DRM_TILCDC_SLAVE_COMPAT module for "ti,tilcdc,slave"
node conversion. The implementation is in tilcdc_slave_compat.c and it
uses tilcdc_slave_compat.dts as a basis for creating a DTS
overlay. The DTS overlay adds an external tda998x encoder to tilcdc
that corresponds to the old tda998x based slave encoder.

Signed-off-by: Jyri Sarha <jsarha@ti.com>
Acked-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
diff --git a/drivers/gpu/drm/tilcdc/Kconfig b/drivers/gpu/drm/tilcdc/Kconfig
index 8394a0b..78beafb 100644
--- a/drivers/gpu/drm/tilcdc/Kconfig
+++ b/drivers/gpu/drm/tilcdc/Kconfig
@@ -12,3 +12,15 @@
 	  Choose this option if you have an TI SoC with LCDC display
 	  controller, for example AM33xx in beagle-bone, DA8xx, or
 	  OMAP-L1xx.  This driver replaces the FB_DA8XX fbdev driver.
+
+config DRM_TILCDC_SLAVE_COMPAT
+	bool "Support device tree blobs using TI LCDC Slave binding"
+	depends on DRM_TILCDC
+	default y
+	select OF_RESOLVE
+	select OF_OVERLAY
+	help
+	  Choose this option if you need a kernel that is compatible
+	  with device tree blobs using the obsolete "ti,tilcdc,slave"
+	  binding. If you find "ti,tilcdc,slave"-string from your DTB,
+	  you probably need this. Otherwise you do not.