cmd: remoteproc: Allow list command to print the probed devices

'rproc list' is currently allowed only after probing all the
available remoteproc devices. Given that 'rproc init' is updated
to probe and initialize devices individually, allow the 'rproc list'
command to print all probed devices at any point.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>