clocksource: Add clocksource id for arm arch counter

Add clocksource id to the ARM generic counter so that it can be easily
identified from callers such as ptp_kvm.

Cc: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Jianyong Wu <jianyong.wu@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20201209060932.212364-6-jianyong.wu@arm.com

drivers/clocksource/arm_arch_timer.c

@@ -16,6 +16,7 @@
 #include <linux/cpu_pm.h>
 #include <linux/clockchips.h>
 #include <linux/clocksource.h>
+#include <linux/clocksource_ids.h>
 #include <linux/interrupt.h>
 #include <linux/of_irq.h>
 #include <linux/of_address.h>
@@ -191,6 +192,7 @@ static u64 arch_counter_read_cc(const struct cyclecounter *cc)
 
 static struct clocksource clocksource_counter = {
 	.name	= "arch_sys_counter",
+	.id	= CSID_ARM_ARCH_COUNTER,
 	.rating	= 400,
 	.read	= arch_counter_read,
 	.mask	= CLOCKSOURCE_MASK(56),

include/linux/clocksource_ids.h

@@ -5,6 +5,7 @@
 /* Enum to give clocksources a unique identifier */
 enum clocksource_ids {
 	CSID_GENERIC		= 0,
+	CSID_ARM_ARCH_COUNTER,
 	CSID_MAX,
 };