python3: fix build on softfloat mips

python3: fix build on softfloat mips

This patch originally only meant to correct the python3 build for mips
with softfloat, as the original test only checked for mips hardfloat.

Replaced custom C Program for triplet detection with autotools triplet
detection.

Signed-off-by: Matthias Schoepfer <matthias.schoepfer@ithinx.io>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>