ptp: add ptp virtual clock driver framework

This patch is to add ptp virtual clock driver framework
utilizing timecounter/cyclecounter.

The patch just exports two essential APIs for PTP driver.

- ptp_vclock_register()
- ptp_vclock_unregister()

Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/ptp_clock_kernel.h

@@ -11,7 +11,9 @@
 #include <linux/device.h>
 #include <linux/pps_kernel.h>
 #include <linux/ptp_clock.h>
+#include <linux/timecounter.h>
 
+#define PTP_CLOCK_NAME_LEN	32
 /**
  * struct ptp_clock_request - request PTP clock event
  *
@@ -134,7 +136,7 @@ struct ptp_system_timestamp {
 
 struct ptp_clock_info {
 	struct module *owner;
-	char name[16];
+	char name[PTP_CLOCK_NAME_LEN];
 	s32 max_adj;
 	int n_alarm;
 	int n_ext_ts;