f2fs: Use bio_for_each_folio_all() in __has_merged_page()

f2fs: Use bio_for_each_folio_all() in __has_merged_page()

Iterate over each folio rather than each page.  Convert
f2fs_compress_control_page() to f2fs_compress_control_folio() since
this is the only caller.  Removes a reference to page->mapping which
is going away soon as well as calls to fscrypt_is_bounce_page() and
fscrypt_pagecache_page().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>