mm/page_reporting: export reporting order as module parameter

The macro PAGE_REPORTING_MIN_ORDER is defined as the page reporting
threshold.  It can't be adjusted at runtime.

This introduces a variable (@page_reporting_order) to replace the marcro
(PAGE_REPORTING_MIN_ORDER).  MAX_ORDER is assigned to it initially,
meaning the page reporting is disabled.  It will be specified by driver if
valid one is provided.  Otherwise, it will fall back to @pageblock_order.
It's also exported so that the page reporting order can be adjusted at
runtime.

Link: https://lkml.kernel.org/r/20210625014710.42954-3-gshan@redhat.com


Signed-off-by: Gavin Shan <gshan@redhat.com>
Suggested-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>