video: Hitachi panel: Drop bogus dependency on CONFIG_VIDEO

The Hitachi tx18d42vm LCD panel driver is really just initialising the
device, using bitbanged SPI, during operation there is nothing to do.
This makes the driver self contained, so drop the bogus dependency on
the legacy CONFIG_VIDEO.

This avoids the warning when building Chuwi_V7_CW0825_defconfig, since
we switched to DM_VIDEO recently.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>