m68k: mm: Convert init_pointer_table() to use ptdescs

m68k: mm: Convert init_pointer_table() to use ptdescs

Motorola uses init_pointer_table() for page tables, so it should be using
struct ptdesc, not struct page.

This helps us prepare to allocate ptdescs as their own memory
descriptor, and prepares to remove a user of page->lru.

Signed-off-by: "Vishal Moola (Oracle)" <vishal.moola@gmail.com>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/20250611001255.527952-4-vishal.moola@gmail.com
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>