struct rproc has a device_d dev field, but so far it was unregistered.
The implementation had a few downsides:

- dev_printf prints NULL, because the unique_name of the device is NULL
- The name used by firmwareload is the device tree node's name, which
  might be unnecessarily verbose, e.g. mlahb:m4@10000000.of
- All remoteproc devices are given the same (unused) name and index

Fix these by registering a device for the remoteproc and using it where
appropriate. While at it, allow the remoteproc name to come from a
device tree alias as well.

This breaks user behavior in that firmwareload now uses the alias or
remoteprocN to reference the remoteproc instance. This is probably
acceptable as the driver is a very recent addition.

Cc: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Ahmad Fatoum <ahmad@a3f.at>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>