mm/khugepaged: convert alloc_charge_hpage() to use folios

mm/khugepaged: convert alloc_charge_hpage() to use folios

Also remove count_memcg_page_event now that its last caller no longer uses
it and reword hpage_collapse_alloc_page() to hpage_collapse_alloc_folio().

This removes 1 call to compound_head() and helps convert khugepaged to
use folios throughout.

Link: https://lkml.kernel.org/r/20231020183331.10770-5-vishal.moola@gmail.com
Signed-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Reviewed-by: Rik van Riel <riel@surriel.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>