llext: Add parameters to arch_elf_relocate

The RISC-V port of llext requires additional parameters for
handling non-adjacent HI20/LO12 relocations in arch_elf_relocate():
the current extension (struct llext), the current extension loader
(struct llext_loader), the current section header (elf_shdr_t) and
the current symbol (elf_sym_t).
This changes the signature of arch_elf_relocate accordingly.

Signed-off-by: Eric Ackermann <eric.ackermann@cispa.de>