nfit, address-range-scrub: determine one platform max_ars value

acpi_nfit_query_poison() is awkward in that it requires an nfit_spa
argument in order to determine what max_ars value to use. Instead probe
for the minimum max_ars across all scrub-capable ranges in the system
and drop the nfit_spa argument.

This enables a larger rework / simplification of the ARS state machine
whereby the status can be retrieved once and then iterated over all
address ranges to reap completions.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/acpi/nfit/nfit.h

@@ -197,10 +197,10 @@ struct acpi_nfit_desc {
 	struct device *dev;
 	u8 ars_start_flags;
 	struct nd_cmd_ars_status *ars_status;
-	size_t ars_status_size;
 	struct work_struct work;
 	struct list_head list;
 	struct kernfs_node *scrub_count_state;
+	unsigned int max_ars;
 	unsigned int scrub_count;
 	unsigned int scrub_mode;
 	unsigned int cancel:1;