mm/vma: small VMA lock cleanups

mm/vma: small VMA lock cleanups

We declare vma_start_read() as a static function in mm/mmap_lock.c, so
there is no need to provide a stub for !CONFIG_PER_VMA_LOCK.

__is_vma_write_locked() is declared in a header and should therefore be
static inline.

Put parens around (refcnt & VMA_LOCK_OFFSET) in is_vma_writer_only() to
make precedence clear.

Link: https://lkml.kernel.org/r/20251024090902.1118174-1-lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Liam Howlett <liam.howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>