media: allegro: lookup VCU settings

The VCU provides information about its configuration in a dedicated
register space. These settings include, for example, the expected clock
rates and the configuration of the encoder buffer. In the device tree,
the settings are described by the "xlnx,vcu-settings" compatible.

The settings are needed to correctly configure the clocks and the
encoder buffer.

Lookup the VCU settings in the device tree and make it accessible to the
driver via a regmap.

Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>