mm: Move may_expand_vm() check in mmap_region()

mm: Move may_expand_vm() check in mmap_region()

The may_expand_vm() check requires the count of the pages within the
munmap range.  Since this is needed for accounting and obtained later,
the reodering of ma_expand_vm() to later in the call stack, after the
vma munmap struct (vms) is initialised and the gather stage is
potentially run, will allow for a single loop over the vmas.  The gather
sage does not commit any work and so everything can be undone in the
case of a failure.

The MAP_FIXED page count is available after the vms_gather_munmap_vmas()
call, so use it instead of looping over the vmas twice.

Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>