ti_config_fragments: enable DRM legacy mode

GPU driver needs DRM legacy mmap APIs. Enable DRM legacy and VM config
options but do not include any legacy drivers.

Signed-off-by: Anand Balagopalakrishnan <anandb@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Jyri Sarha <jsarha@ti.com>
[praneeth@ti.com: rebase from graphics-ti-linux-4.14.y]
Signed-off-by: Praneeth Bajjuri <praneeth@ti.com>

ti_config_fragments/audio_display.cfg

@@ -27,6 +27,10 @@ CONFIG_DRM_TI_TFP410=y
 CONFIG_DRM_TOSHIBA_TC358767=y
 CONFIG_DRM_PANEL_SIMPLE=y
 
+# SGX driver needs legacy support
+CONFIG_DRM_LEGACY=y
+CONFIG_DRM_VM=y
+
 # tilcdc
 
 CONFIG_DRM_I2C_NXP_TDA998X=y