The si4713 supports several RDS features not yet implemented in the driver.

This patch adds the missing RDS functionality to the list of RDS controls.

The ALT_FREQS control is a compound control containing an array of up
to 25 (the maximum according to the RDS standard) frequencies. To support
that the V4L2_CTRL_TYPE_U32 was added.
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Cc: Eduardo Valentin <edubezval@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>