powerpc: Add support for fmaf128() in hardware

Adds a POWER9 version of fmaf128 that uses the xsmaddqp
instruction.

Co-authored-by: Tulio Magno Quites Machado Filho <tuliom@linux.ibm.com>
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>