x86/mm: Override mfn_to_page() and page_to_mfn() to use mfn_t

x86/mm: Override mfn_to_page() and page_to_mfn() to use mfn_t

To avoid breaking the build elsewhere, the l{1..4}e_{from,get}_page() macros
are switched to using __mfn_to_page() and __page_to_mfn().

Most changes are wrapping or removing _mfn()/mfn_x() from existing callsites.

However, {alloc,free}_l1_table() are switched to using __map_domain_page(), as
their pfn parameters are otherwise unused.  get_page() has one pfn->mfn
correction in a printk(), and __get_page_type()'s IOMMU handling has its gfn
calculation broken out for clarity.

No functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>