ARM: dts: imx6: RDU2: adjust audio devices nomenclature

This adds a "HPA1" prefix to the amplifiers on both audio cards, this is
done in order to get more consistency for userspace running on RDU2 and
RDU3, where we have two amplifiers on a single card device in the "Zest"
configuration.

Also adjust the card names to the new standard expected by userspace.

Signed-off-by: Cory Tusar <cory.tusar@zii.aero>
[adjusted commit message]
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>