arm: k3: Add support for loading non linux remote cores

Add MAIN domain R5FSS0 remoteproc support from spl. This enables
loading the elf firmware in SPL and starting the remotecore.

In order to start the core, there should be a file with path
"/lib/firmware/j7-main-r5f0_0-fw" under filesystem
of respective boot mode.

Signed-off-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
[Guard start_non_linux_remote_cores under CONFIG_FS_LOADER]
Signed-off-by: Andreas Dannenberg <dannenberg@ti.com>