shmem: convert shmem_alloc_hugepage() to use vma_alloc_folio()

shmem: convert shmem_alloc_hugepage() to use vma_alloc_folio()

Patch series "Folio patches for 5.19", v2.

This patch (of 26):

For now, return the head page of the folio, but remove use of the old
alloc_pages_vma() API.

Link: https://lkml.kernel.org/r/20220504182857.4013401-1-willy@infradead.org
Link: https://lkml.kernel.org/r/20220504182857.4013401-2-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>