x86/cpu: Add AVX512_FP16 cpu feature

x86/cpu: Add AVX512_FP16 cpu feature

AVX512 Half-precision floating point (FP16) has better performance
compared to FP32 if the presicion or magnitude requirements are met.
It's defined as CPUID.(EAX=7,ECX=0):EDX[bit 23].

Refer to
https://software.intel.com/content/www/us/en/develop/download/\
intel-architecture-instruction-set-extensions-programming-reference.html

Signed-off-by: Cathy Zhang <cathy.zhang@intel.com>
Message-Id: <20201216224002.32677-1-cathy.zhang@intel.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>