libnvdimm, nfit: centralize command status translation

The return value from an 'ndctl_fn' reports the command execution
status, i.e. was the command properly formatted and was it successfully
submitted to the bus provider.  The new 'cmd_rc' parameter allows the bus
provider to communicate command specific results, translated into
common error codes.

Convert the ARS commands to this scheme to:

1/ Consolidate status reporting

2/ Prepare for for expanding ars unit test cases

3/ Make the implementation more generic

Cc: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
diff --git a/drivers/acpi/nfit.h b/drivers/acpi/nfit.h
index 6689b0a..f45b7d9 100644
--- a/drivers/acpi/nfit.h
+++ b/drivers/acpi/nfit.h
@@ -47,8 +47,15 @@
 };
 
 enum {
-	ND_BLK_READ_FLUSH = 1,
-	ND_BLK_DCR_LATCH = 2,
+	NFIT_BLK_READ_FLUSH = 1,
+	NFIT_BLK_DCR_LATCH = 2,
+	NFIT_ARS_STATUS_DONE = 0,
+	NFIT_ARS_STATUS_BUSY = 1 << 16,
+	NFIT_ARS_STATUS_NONE = 2 << 16,
+	NFIT_ARS_STATUS_INTR = 3 << 16,
+	NFIT_ARS_START_BUSY = 6,
+	NFIT_ARS_CAP_NONE = 1,
+	NFIT_ARS_F_OVERFLOW = 1,
 };
 
 struct nfit_spa {