x86/bugs: Use VM_CLEAR_CPU_BUFFERS in VMX as well

x86/bugs: Use VM_CLEAR_CPU_BUFFERS in VMX as well

TSA mitigation:

  d8010d4ba43e ("x86/bugs: Add a Transient Scheduler Attacks mitigation")

introduced VM_CLEAR_CPU_BUFFERS for guests on AMD CPUs. Currently on Intel
CLEAR_CPU_BUFFERS is being used for guests which has a much broader scope
(kernel->user also).

Make mitigations on Intel consistent with TSA. This would help handling the
guest-only mitigations better in future.

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
[sean: make CLEAR_CPU_BUF_VM mutually exclusive with the MMIO mitigation]
Acked-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Brendan Jackman <jackmanb@google.com>
Link: https://patch.msgid.link/20251113233746.1703361-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>