Correct pmap_copy()'s method for extracting the physical address of a
2/4MB page from a PDE. Specifically, change it to use PG_PS_FRAME,
not PG_FRAME, to extract the physical address of a 2/4MB page from a
PDE.

Change the last argument passed to pmap_pv_insert_pde() from a
vm_page_t representing the first 4KB page of a 2/4MB page to the
vm_paddr_t of the 2/4MB page. This avoids an otherwise unnecessary
conversion from a vm_paddr_t to a vm_page_t in pmap_copy().