KVM: VMX: Refactor 32-bit PSE PT creation to avoid using MMU macro

Compute the number of PTEs to be filled for the 32-bit PSE page tables
using the page size and the size of each entry.  While using the MMU's
PT32_ENT_PER_PAGE macro is arguably better in isolation, removing VMX's
usage will allow a future namespacing cleanup to move the guest page
table macros into paging_tmpl.h, out of the reach of code that isn't
directly related to shadow paging.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220614233328.3896033-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>