timekeeper: try to sync base time between cpus

kernel-src/include/kernel/timekeeper.h

@@ -29,6 +29,8 @@ void timekeeper_init(void);
 // spins waiting for us to pass
 void timekeeper_wait_us(time_t us);
 
+void timekeeper_sync(void);
+
 timespec_t timekeeper_timefromboot(void);
 timespec_t timekeeper_time(void);
 

kernel-src/include/x86-64/arch/cpu.h

@@ -30,6 +30,7 @@ typedef struct cpu_t {
 	timekeeper_source_info_t *timekeeper_source_info;
 	time_t timekeeper_source_base_ticks;
 	time_t timekeeper_source_tick_offset;
+	isr_t *timekeeper_sync_isr;
 
 	isr_t isr[MAX_ISR_COUNT];
 	bool intstatus;