configs: j721e_evm_r5: Enable R5F remoteproc support

Enable R5F remoteproc support in R5 defconfig so that R5s can
be started in SPL. While at it enable the SPL_FS_EXT4 config
option to load the firmwares from file system.

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