nVMX x86: check posted-interrupt control on vmentry of L2

According to section "Checks on VMX Controls" in Intel SDM vol 3C,
the following check needs to be enforced on vmentry of L2 guests:

    If the “process posted interrupts†VM-execution control is 1, the
    following must be true:

      - The “virtual-interrupt delivery†VM-execution control is 1.
      - The “acknowledge interrupt on exit†VM-exit control is 1.
      - The posted-interrupt notification vector has a value in the
      - range 0–255 (bits 15:8 are all 0).
      - Bits 5:0 of the posted-interrupt descriptor address are all 0.
      - The posted-interrupt descriptor address does not set any bits
        beyond the processor's physical-address width.

Signed-off-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Reviewed-by: Karl Heubaum <karl.heubaum@oracle.com>
Message-Id: <20180824000304.19070-3-krish.sadhukhan@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>