KVM: x86: Advertise CPUID.(EAX=7,ECX=2):EDX[5:0] to userspace

The low five bits {INTEL_PSFD, IPRED_CTRL, RRSBA_CTRL, DDPD_U, BHI_CTRL}
advertise the availability of specific bits in IA32_SPEC_CTRL. Since KVM
dynamically determines the legal IA32_SPEC_CTRL bits for the underlying
hardware, the hard work has already been done. Just let userspace know
that a guest can use these IA32_SPEC_CTRL bits.

The sixth bit (MCDT_NO) states that the processor does not exhibit MXCSR
Configuration Dependent Timing (MCDT) behavior. This is an inherent
property of the physical processor that is inherited by the virtual
CPU. Pass that information on to userspace.

Signed-off-by: Jim Mattson <jmattson@google.com>
Reviewed-by: Chao Gao <chao.gao@intel.com>
Link: https://lore.kernel.org/r/20231024001636.890236-1-jmattson@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>