nSVM: Check for reserved encodings of TLB_CONTROL in nested VMCB

According to section "TLB Flush" in APM vol 2,

    "Support for TLB_CONTROL commands other than the first two, is
     optional and is indicated by CPUID Fn8000_000A_EDX[FlushByAsid].

     All encodings of TLB_CONTROL not defined in the APM are reserved."

Signed-off-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
Message-Id: <20210920235134.101970-3-krish.sadhukhan@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>