MIPS: ELF: Unify __MIPS_O32_FP64_MUST_BE_ZERO definitions

Signed-off-by: Maciej W. Rozycki <macro@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/13244/


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