Use uint64_t for time types

Unfortunately 'unsigned long long' and 'uint64_t' are not necessarily
compatible on 64-bit machines. Use the correct typedef instead of
writing the supposed type out in full.

Signed-off-by: Simon Glass <sjg@chromium.org>

include/common.h

@@ -766,7 +766,7 @@ void	invalidate_dcache_all(void);
 void	invalidate_icache_all(void);
 
 /* arch/$(ARCH)/lib/ticks.S */
-unsigned long long get_ticks(void);
+uint64_t get_ticks(void);
 void	wait_ticks    (unsigned long);
 
 /* arch/$(ARCH)/lib/time.c */