remoteproc: Move Elf related functions to separate file

Prepare for introduction of custom firmware loaders by
moving all ELF related handling into a separate file.

The functions: rproc_find_rsc_table(), rproc_fw_sanity_check(),
rproc_find_rsc_table() and rproc_get_boot_addr() are moved
to the new file remoteproc_elf_loader.c. The function
rproc_da_to_va() is made non-static and is declared in
remoteproc_internal.h

No functional changes are introduced in this patch.

Signed-off-by: Sjur Brændeland <sjur.brandeland@stericsson.com>
[ohad: rebase, fix kerneldoc, put prototypes in remoteproc_internal.h]
Signed-off-by: Ohad Ben-Cohen <ohad@wizery.com>