MIPS: ELF: Unify ABI classification macros

Remove a duplicate o32 `elf_check_arch' implementation, move all macro
variants to <asm/elf.h> and define them unconditionally under indvidual
names, substituting alias `elf_check_arch' definitions in variant code.

Signed-off-by: Maciej W. Rozycki <macro@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/13245/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>