remoteproc: k3-r5: Use verified image address

remoteproc: k3-r5: Use verified image address

After ti_secure_image_post_process() authenticates the image, it may
relocate it to a different memory location and update image_addr to
point to the verified image.

However, rproc_elf_load_image() and rproc_elf_get_boot_addr() were
still using the original "addr" parameter, potentially operating on
the unverified or stale image location instead of the authenticated
image.

Use image_addr (cast to ulong to match function signatures) after
authentication to ensure all operations work with the verified image.

Signed-off-by: Philippe Schenker <philippe.schenker@impulsing.ch>