arm64: defconfig: Enable ITE_IT66121 HDMI transmitter

Enable CONFIG_DRM_ITE_IT66121.

ILITEK ITE-IT66121 is an HDMI transmitter, which takes parallel video
signals (DPI) as input. It is being used on TI's AM625 SoC based
BeaglePlay platform[0].

[0]: https://beagleboard.org/playSigned-off-by: Aradhya Bhatia <a-bhatia1@ti.com>
Link: https://lore.kernel.org/r/20230809084559.17322-7-a-bhatia1@ti.comSigned-off-by: Nishanth Menon <nm@ti.com>

arch/arm64/configs/defconfig

@@ -826,6 +826,7 @@ CONFIG_DRM_PANEL_VISIONOX_VTDR6130=m
 CONFIG_DRM_LONTIUM_LT8912B=m
 CONFIG_DRM_LONTIUM_LT9611=m
 CONFIG_DRM_LONTIUM_LT9611UXC=m
+CONFIG_DRM_ITE_IT66121=m
 CONFIG_DRM_NWL_MIPI_DSI=m
 CONFIG_DRM_PARADE_PS8640=m
 CONFIG_DRM_SII902X=m