remoteproc: code cleanup of resource parsing

Combine the almost identical functions rproc_handle_virtio_rsc
and rproc_handle_boot_rsc.

Signed-off-by: Sjur Brændeland <sjur.brandeland@stericsson.com>
Acked-by: Ido Yariv <ido@wizery.com>
[small terminology and style changes]
Signed-off-by: Ohad Ben-Cohen <ohad@wizery.com>