region_is_ram() is used to prevent the establishment of aliased mappings
to physical "System RAM" with incompatible cache settings.  However, it
uses "-1" to indicate both "unknown" memory ranges (ranges not described
by platform firmware) and "mixed" ranges (where the parameters describe
a range that partially overlaps "System RAM").

Fix this up by explicitly tracking the "unknown" vs "mixed" resource
cases and returning REGION_INTERSECTS, REGION_MIXED, or REGION_DISJOINT.
This re-write also adds support for detecting when the requested region
completely eclipses all of a resource.  Note, the implementation treats
overlaps between "unknown" and the requested memory type as
REGION_INTERSECTS.

Finally, other memory types can be passed in by name, for now the only
usage "System RAM".

Suggested-by: Luis R. Rodriguez <redacted>
Reviewed-by: Toshi Kani <redacted>
Signed-off-by: Dan Williams <redacted>
---
 include/linux/mm.h |    9 +++++++-
 kernel/resource.c  |   61 +++++++++++++++++++++++++++++++---------------------
 2 files changed, 44 insertions(+), 26 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 2e872f92dbac..84b05ebedb2d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h

@@ -369,7 +369,14 @@ static inline int put_page_unless_one(struct page *page)
 }
 
 extern int page_is_ram(unsigned long pfn);
-extern int region_is_ram(resource_size_t phys_addr, unsigned long size);
+
+enum {