mm: Start tracking VMAs with maple tree

mm: Start tracking VMAs with maple tree

Start tracking the VMAs with the new maple tree structure in parallel
with the rb_tree.  Add debug and trace events for maple tree operations
and duplicate the rb_tree that is created on forks into the maple tree.

The maple tree is added to the mm_struct including the mm_init struct,
added support in required mm/mmap functions, added tracking in
kernel/fork for process forking, and used to find the unmapped_area and
checked against what the rbtree finds.

Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>