remoteproc: fix missing CONFIG_FW_LOADER configurations

commit e121aefa7d9f10eee5cf26ed47129237a05d940b upstream.

Remoteproc requires user space firmware loading support, so
let's select FW_LOADER explicitly to avoid painful misconfigurations
(which only show up in runtime).

Reported-by: Mark Grosen <mgrosen@ti.com>
Signed-off-by: Ohad Ben-Cohen <ohad@wizery.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>