mm: cma: add functions to get region pages counters

mm: cma: add functions to get region pages counters

Here are two functions that provide interface to compute/get used size and
size of biggest free chunk in cma region.  Add that information to
debugfs.

[[email protected]: move debug code from cma.c into cma_debug.c]
[[email protected]: move code from cma_get_used() and cma_get_maxchunk() to cma_used_get() and cma_maxchunk_get()]
Signed-off-by: Dmitry Safonov <[email protected]>
Signed-off-by: Stefan Strogin <[email protected]>
Acked-by: Michal Nazarewicz <[email protected]>
Cc: Marek Szyprowski <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Pintu Kumar <[email protected]>
Cc: Weijie Yang <[email protected]>
Cc: Laurent Pinchart <[email protected]>
Cc: Vyacheslav Tyrtov <[email protected]>
Cc: Aleksei Mateosian <[email protected]>
Signed-off-by: Stefan Strogin <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>