ARC is the only arch with unsigned long type (vs. struct page *).
Historically this was done to avoid the page_address() calls in various
arch hooks which need to get the virtual/logical address of the table.

Some arches alternately define it as pte_t *, and is as efficient as
unsigned long (generated code doesn't change)
Suggested-by: NKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: NVineet Gupta <vgupta@synopsys.com>