devicetree: bindings: Document Krait performance monitor units (PMU)

Document the Krait PMU compatible string.

Cc: <devicetree@vger.kernel.org>
Signed-off-by: NStephen Boyd <sboyd@codeaurora.org>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

Documentation/devicetree/bindings/arm/pmu.txt

@@ -16,7 +16,14 @@ Required properties:
 	"arm,arm11mpcore-pmu"
 	"arm,arm1176-pmu"
 	"arm,arm1136-pmu"
-- interrupts : 1 combined interrupt or 1 per core.
+	"qcom,krait-pmu"
+- interrupts : 1 combined interrupt or 1 per core. If the interrupt is a per-cpu
+               interrupt (PPI) then 1 interrupt should be specified.
+
+Optional properties:
+
+- qcom,no-pc-write : Indicates that this PMU doesn't support the 0xc and 0xd
+                     events.
 
 Example: