MIPS: module: Unify rel & rela reloc handling

The module load code has previously had entirely separate
implementations for rel & rela style relocs, which unnecessarily
duplicates a whole lot of code. Unify the implementations of both types
of reloc, sharing the bulk of the code.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/15832/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>