ARCv2: perf: Finally introduce HS perf unit

With all features in place, the ARC HS pct block can now be effectively
allowed to be probed/used

Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

Documentation/devicetree/bindings/arc/archs-pct.txt

@@ -0,0 +1,17 @@
+* ARC HS Performance Counters
+
+The ARC HS can be configured with a pipeline performance monitor for counting
+CPU and cache events like cache misses and hits. Like conventional PCT there
+are 100+ hardware conditions dynamically mapped to upto 32 counters.
+It also supports overflow interrupts.
+
+Required properties:
+
+- compatible : should contain
+	"snps,archs-pct"
+
+Example:
+
+pmu {
+        compatible = "snps,archs-pct";
+};