arm: allwinner: Garbage collect a10_hdmi driver

It was disconnected 5 years ago in 4573cd3914d7
("arm: allwinner: Disconnect A10/A20 HDMI driver") as it wasn't working.

Sponsored by: Beckhoff Automation GmbH & Co. KG
Reviewed by: andrew
Differential Revision: https://reviews.freebsd.org/D39117