firmware: imx: Save channel name for further use

We want to request / free channels on demand later in order
to save power.

For this for each channel we save the name and use it to
reference the channel later.

Signed-off-by: Daniel Baluta <daniel.baluta@nxp.com>
Reviewed-by: Paul Olaru <paul.olaru@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>