fs: Add FOP_HUGE_PAGES

fs: Add FOP_HUGE_PAGES

Instead of checking for specific file_operations, add a bit to
file_operations which denotes a file that only contain hugetlb pages.
This lets us make hugetlbfs_file_operations static, and removes
is_file_shm_hugepages() completely.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Link: https://lore.kernel.org/r/20240407201122.3783877-1-willy@infradead.org
Signed-off-by: Christian Brauner <brauner@kernel.org>