KVM: nVMX: move check_vmentry_postreqs() call to nested_vmx_enter_non_root_mode()

In preparation of supporting checkpoint/restore for nested state,
commit ca0bde28 ("kvm: nVMX: Split VMCS checks from nested_vmx_run()")
modified check_vmentry_postreqs() to only perform the guest EFER
consistency checks when nested_run_pending is true.  But, in the
normal nested VMEntry flow, nested_run_pending is only set after
check_vmentry_postreqs(), i.e. the consistency check is being skipped.

Alternatively, nested_run_pending could be set prior to calling
check_vmentry_postreqs() in nested_vmx_run(), but placing the
consistency checks in nested_vmx_enter_non_root_mode() allows us
to split prepare_vmcs02() and interleave the preparation with
the consistency checks without having to change the call sites
of nested_vmx_enter_non_root_mode().  In other words, the rest
of the consistency check code in nested_vmx_run() will be joining
the postreqs checks in future patches.

Fixes: ca0bde28 ("kvm: nVMX: Split VMCS checks from nested_vmx_run()")
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Jim Mattson <jmattson@google.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>