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/play

Signed-off-by: Aradhya Bhatia <a-bhatia1@ti.com>
Link: https://lore.kernel.org/r/20230809084559.17322-7-a-bhatia1@ti.com
Signed-off-by: Nishanth Menon <nm@ti.com>