remoteproc: Pass struct fw to load_segments and find_rsc_table.

Prepare for introduction of custom firmware loaders by changing
the functions rproc_find_rcs_table() and rproc_load_segments()
to use struct firmware as parameter.

When the custom loader framework is introduced all calls into
the firmware specific function must use struct firmware as
parameter.

Signed-off-by: Sjur Brændeland <sjur.brandeland@stericsson.com>
Signed-off-by: Ohad Ben-Cohen <ohad@wizery.com>