mm/mmap: refactor locking out of __vma_adjust()

Move the locking into vma_prepare() and vma_complete() for use elsewhere

Link: https://lkml.kernel.org/r/20230120162650.984577-41-Liam.Howlett@oracle.com


Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>