FROMLIST: BACKPORT: mm/page_alloc: Add page->buddy_list and page->pcp_list

The page allocator uses page->lru for storing pages on either buddy or
PCP lists. Create page->buddy_list and page->pcp_list as a union with
page->lru. This is simply to clarify what type of list a page is on
in the page allocator.

No functional change intended.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Link: https://lore.kernel.org/all/20220420095906.27349-2-mgorman@techsingularity.net/



Bug: 230899966
Signed-off-by: Minchan Kim <minchan@google.com>
Change-Id: Ieef253fa28c2a411008da64b38716f6401a66961