x86/paging: Rename paging_mark_pfn_dirty() and use pfn_t

x86/paging: Rename paging_mark_pfn_dirty() and use pfn_t

paging_mark_gfn_dirty() actually takes a pfn, even by paramter name.  Rename
the function and alter the type to pfn_t to match.

Push pfn_t into the LOGDIRTY_IDX() macros, and clean up a couple of local
variable types in paging_mark_pfn_dirty().

Leave an explicit comment in vmx_vcpu_flush_pml_buffer() when we intentally
perform a straight conversion from gfn to pfn.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Tim Deegan <tim@xen.org>