x86/mm/pat: Rename pat_rbtree.c to pat_interval.c

Considering the previous changes, this is a more proper name.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lkml.kernel.org/r/20191121011601.20611-5-dave@stgolabs.net


Signed-off-by: Ingo Molnar <mingo@kernel.org>