[PowerPC] Support test data class intrinsic of 128-bit float

We've exploited test data class instructions introduced in ISA 3.0.
This change unifies the scalar intrinsics into ppc_test_data_class
and add support for 128-bit precision float values using xststdcqp.

Vector versions of the intrinsic can't be unified because they return
vector int instead of int.

Reviewed By: shchenz

Differential Revision: https://reviews.llvm.org/D138105