KVM: x86: Replace "cr3" with "pgd" in "new cr3/pgd" related code

Rename functions and variables in kvm_mmu_new_cr3() and related code to
replace "cr3" with "pgd", i.e. continue the work started by commit
727a7e27

 ("KVM: x86: rename set_cr3 callback and related flags to
load_mmu_pgd").  kvm_mmu_new_cr3() and company are not always loading a
new CR3, e.g. when nested EPT is enabled "cr3" is actually an EPTP.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200320212833.3507-37-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>