KVM: x86: Advertise AVX512 Bit Matrix Multiply (BMM) to userspace

KVM: x86: Advertise AVX512 Bit Matrix Multiply (BMM) to userspace

Advertise AVX512 Bit Matrix Multiply (BMM) and Bit Reversal instructions to
userspace via CPUID leaf 0x80000021_EAX[23]. This feature enables bit
matrix multiply operations and bit reversal.  Like most AVX instructions,
there are no intercept controls for individual instructions, and no extra
work is needed in KVM to enable correct execution of the instructions in
the guest.

The instructions and CPUID feature are first described in:

  AMD64 Bit Matrix Multiply and Bit Reversal Instructions
  Publication #69192 Revision: 1.00
  Issue Date: January 2026

While at it, reorder PREFETCHI in KVM's initialization sequence to match
the CPUID bit position order for better organization.

Signed-off-by: Nikunj A Dadhania <nikunj@amd.com>
Link: https://patch.msgid.link/20260210053511.1612505-1-nikunj@amd.com
[sean: massage changelog]
Signed-off-by: Sean Christopherson <seanjc@google.com>