KVM: nVMX: Check Host Address Space Size on vmentry of nested guests

According to section "Checks Related to Address-Space Size" in Intel SDM
vol 3C, the following checks are performed on vmentry of nested guests:

    If the logical processor is outside IA-32e mode (if IA32_EFER.LMA = 0)
    at the time of VM entry, the following must hold:
	- The "IA-32e mode guest" VM-entry control is 0.
	- The "host address-space size" VM-exit control is 0.

    If the logical processor is in IA-32e mode (if IA32_EFER.LMA = 1) at the
    time of VM entry, the "host address-space size" VM-exit control must be 1.

    If the "host address-space size" VM-exit control is 0, the following must
    hold:
	- The "IA-32e mode guest" VM-entry control is 0.
	- Bit 17 of the CR4 field (corresponding to CR4.PCIDE) is 0.
	- Bits 63:32 in the RIP field are 0.

    If the "host address-space size" VM-exit control is 1, the following must
    hold:
	- Bit 5 of the CR4 field (corresponding to CR4.PAE) is 1.
	- The RIP field contains a canonical address.

    On processors that do not support Intel 64 architecture, checks are
    performed to ensure that the "IA-32e mode guest" VM-entry control and the
    "host address-space size" VM-exit control are both 0.

Signed-off-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
Reviewed-by: Karl Heubaum <karl.heubaum@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>