target/i386: Export BHI_NO bit to guests

target/i386: Export BHI_NO bit to guests

Branch History Injection (BHI) is a CPU side-channel vulnerability, where
an attacker may manipulate branch history before transitioning from user
to supervisor mode or from VMX non-root/guest to root mode. CPUs that set
BHI_NO bit in MSR IA32_ARCH_CAPABILITIES to indicate no additional
mitigation is required to prevent BHI.

Make BHI_NO bit available to guests.

Tested-by: Xuelian Guo <xuelian.guo@intel.com>
Signed-off-by: Tao Su <tao1.su@linux.intel.com>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Link: https://lore.kernel.org/r/20250121020650.1899618-3-tao1.su@linux.intel.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>