KVM: x86: expose AVX512_BF16 feature to guest

mainline inclusion
from mainline-v5.3-rc1
commit 0b774629
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I3YAEG
CVE: NA

-----------------------------

AVX512 BFLOAT16 instructions support 16-bit BFLOAT16 floating-point
format (BF16) for deep learning optimization.

Intel adds AVX512 BFLOAT16 feature in CooperLake, which is CPUID.7.1.EAX[5].

Detailed information of the CPUID bit can be found here,
https://software.intel.com/sites/default/files/managed/c5/15/\


architecture-instruction-set-extensions-programming-reference.pdf.

Signed-off-by: Jing Liu <jing2.liu@linux.intel.com>
[Fix type mismatch in min, changing constant "1" to "1u". - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Jingyi Wang <wangjingyi11@huawei.com>
Reviewed-by: Keqian Zhu <zhukeqian1@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>