fs/dax: make it possible to check dev dax support without a VMA

fs/dax: make it possible to check dev dax support without a VMA

This is a prerequisite for adapting those filesystems to use the
.mmap_prepare() hook for mmap()'ing which invoke this check as this hook
does not have access to a VMA pointer.

To effect this, change the signature of daxdev_mapping_supported() and
update its callers (ext4 and xfs mmap()'ing hook code).

Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Link: https://lore.kernel.org/b09de1e8544384074165d92d048e80058d971286.1750099179.git.lorenzo.stoakes@oracle.com
Signed-off-by: Christian Brauner <brauner@kernel.org>