KVM: x86: Advertise MOVRS CPUID to userspace

KVM: x86: Advertise MOVRS CPUID to userspace

Define the feature flag for MOVRS and advertise support to userspace when
the feature is supported by the host.

MOVRS is a new set of instructions introduced in the Intel platform
Diamond Rapids, to provide load instructions that carry a read-shared
hint.

Functionally, MOVRS family is equivalent to existing load instructions,
but its read-shared hint indicates that the source memory location is
likely to become read-shared by multiple processors, i.e., read in the
future by at least one other processor before it is written (assuming it
is ever written in the future). This hint could optimize the behavior of
the caches, especially shared caches, for this data for future reads by
multiple processors. Additionally, MOVRS family also includes a software
prefetch instruction, PREFETCHRST2, that carries the same read-shared
hint. [*]

MOVRS family is enumerated by CPUID single-bit (0x7.0x1.EAX[bit 31]).
Since it's on a densely-populated CPUID leaf and some other bits on
this leaf have kernel usages, define this new feature in cpufeatures.h,
but hide it in /proc/cpuinfo due to lack of current kernel usage.

Advertise MOVRS bit to userspace directly. It's safe, since there's no
new VMX controls or additional host enabling required for guests to use
this feature.

[*]: Intel Architecture Instruction Set Extensions and Future Features
     (rev.059).

Tested-by: Xudong Hao <xudong.hao@intel.com>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Link: https://patch.msgid.link/20251120050720.931449-2-zhao1.liu@intel.com
Signed-off-by: Sean Christopherson <seanjc@google.com>