x86/cpu: Add Tremont to the cpu vulnerability whitelist

Add the new cpu family ATOM_TREMONT_D to the cpu vunerability
whitelist. ATOM_TREMONT_D is not affected by X86_BUG_ITLB_MULTIHIT.

ATOM_TREMONT_D might have mitigations against other issues as well, but
only the ITLB multihit mitigation is confirmed at this point.

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>