mm: page_owner: use kstrtobool() to parse bool option

I tried to use page_owner=1 for a while noticed too late it had no effect
as opposed to similar init_on_alloc=1 (these work).

Let's make them consistent.

The change decreses binary size slightly:
   text    data     bss     dec     hex filename
  12408     321      17   12746    31ca mm/page_owner.o.before
  12320     321      17   12658    3172 mm/page_owner.o.after

Link: https://lkml.kernel.org/r/20210401210909.3532086-1-slyfox@gentoo.org


Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>