units: complement the set of Hz units

Currently, Hz units do not have milli, micro and nano Hz coefficients.
Some drivers (IIO especially) use their analogues to calculate
appropriate Hz values. This patch includes them to units.h definitions,
so they can be used from different kernel places.
Signed-off-by: Dmitry Rokosov <ddrokosov@sberdevices.ru>
Link: https://lore.kernel.org/r/20220812165243.22177-3-ddrokosov@sberdevices.ruSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

include/linux/units.h

@@ -20,6 +20,9 @@
 #define PICO	1000000000000ULL
 #define FEMTO	1000000000000000ULL
 
+#define NANOHZ_PER_HZ		1000000000UL
+#define MICROHZ_PER_HZ		1000000UL
+#define MILLIHZ_PER_HZ		1000UL
 #define HZ_PER_KHZ		1000UL
 #define KHZ_PER_MHZ		1000UL
 #define HZ_PER_MHZ		1000000UL