KVM: PPC: Book3S HV: Use __gfn_to_pfn_memslot in HPT page fault handler

This makes the same changes in the page fault handler for HPT guests
that commits 31c8b0d0 ("KVM: PPC: Book3S HV: Use __gfn_to_pfn_memslot()
in page fault handler", 2018-03-01), 71d29f43 ("KVM: PPC: Book3S HV:
Don't use compound_order to determine host mapping size", 2018-09-11)
and 6579804c ("KVM: PPC: Book3S HV: Avoid crash from THP collapse
during radix page fault", 2018-10-04) made for the page fault handler
for radix guests.

In summary, where we used to call get_user_pages_fast() and then do
special handling for VM_PFNMAP vmas, we now call __get_user_pages_fast()
and then __gfn_to_pfn_memslot() if that fails, followed by reading the
Linux PTE to get the host PFN, host page size and mapping attributes.

This also brings in the change from SetPageDirty() to set_page_dirty_lock()
which was done for the radix page fault handler in commit c3856aeb
("KVM: PPC: Book3S HV: Fix handling of large pages in radix page fault
handler", 2018-02-23).

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>