libnvdimm, e820: skip module loading when no type-12

If there are no persistent memory ranges present then don't bother
creating the platform device.  Otherwise, it loads the full libnvdimm
sub-system only to discover no resources present.

Reported-by: Andy Lutomirski <luto@amacapital.net>
Acked-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

arch/x86/kernel/pmem.c

@@ -4,10 +4,22 @@
  */
 #include <linux/platform_device.h>
 #include <linux/module.h>
+#include <linux/ioport.h>
+
+static int found(u64 start, u64 end, void *data)
+{
+	return 1;
+}
 
 static __init int register_e820_pmem(void)
 {
+	char *pmem = "Persistent Memory (legacy)";
 	struct platform_device *pdev;
+	int rc;
+
+	rc = walk_iomem_res(pmem, IORESOURCE_MEM, 0, -1, NULL, found);
+	if (rc <= 0)
+		return 0;
 
 	/*
 	 * See drivers/nvdimm/e820.c for the implementation, this is