KVM: nVMX: Allocate and configure VM{READ,WRITE} bitmaps iff enable_shadow_vmcs

mainline inclusion
from mainline-v5.0-rc1
commit dfae3c03
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I4MKP4


CVE: NA

--------------------------------

...and make enable_shadow_vmcs depend on nested.  Aside from the obvious
memory savings, this will allow moving the relevant code out of vmx.c in
the future, e.g. to a nested specific file.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Jackie Liu <liuyun01@kylinos.cn> #openEuler_contributor
Signed-off-by: Laibin Qiu <qiulaibin@huawei.com>
Reviewed-by: Zenghui Yu <yuzenghui@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>