[PowerPC] Add dense math half-precision floating-point outer-product accumulate to DMR instructions (#133272)
This patch adds the following Dense Math Facility 16-bit half-precision
floating-point calculation instructions: dmxvf16gerx2, dmxvf16gerx2pp,
dmxvf16gerx2pn, dmxvf16gerx2np, dmxvf16gerx2nn, pmdmxvf16gerx2,
pmdmxvf16gerx2pp, pmdmxvf16gerx2pn, pmdmxvf16gerx2np, pmdmxvf16gerx2nn,
along with their corresponding intrinsics and tests.