KVM: x86/mmu: Use gfn_t in kvm_flush_remote_tlbs_range()

Use gfn_t instead of u64 for kvm_flush_remote_tlbs_range()'s parameters,
since gfn_t is the standard type for GFNs throughout KVM.

Opportunistically rename pages to nr_pages to make its role even more
obvious.

No functional change intended.

Signed-off-by: David Matlack <dmatlack@google.com>
Link: https://lore.kernel.org/r/20230126184025.2294823-6-dmatlack@google.com


[sean: convert pages to gfn_t too, and rename]
Signed-off-by: Sean Christopherson <seanjc@google.com>