x86, libnvdimm, pmem: remove global pmem api

Now that all callers of the pmem api have been converted to dax helpers that
call back to the pmem driver, we can remove include/linux/pmem.h and
asm/pmem.h.

Cc: <x86@kernel.org>
Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Toshi Kani <toshi.kani@hpe.com>
Cc: Oliver O'Halloran <oohall@gmail.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

fs/dax.c

@@ -25,7 +25,6 @@
 #include <linux/mm.h>
 #include <linux/mutex.h>
 #include <linux/pagevec.h>
-#include <linux/pmem.h>
 #include <linux/sched.h>
 #include <linux/sched/signal.h>
 #include <linux/uio.h>