units: add the HZ macros

units: add the HZ macros

The macros for the unit conversion for frequency are duplicated in
different places.

Provide these macros in the 'units' header, so they can be reused.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Daniel Lezcano <[email protected]>
Reviewed-by: Christian Eggers <[email protected]>
Reviewed-by: Andy Shevchenko <[email protected]>
Cc: Chanwoo Choi <[email protected]>
Cc: Guenter Roeck <[email protected]>
Cc: Jonathan Cameron <[email protected]>
Cc: Jonathan Cameron <[email protected]>
Cc: Kyungmin Park <[email protected]>
Cc: Lars-Peter Clausen <[email protected]>
Cc: Lukasz Luba <[email protected]>
Cc: Maxime Coquelin <[email protected]>
Cc: Miquel Raynal <[email protected]>
Cc: MyungJoo Ham <[email protected]>
Cc: Peter Meerwald <[email protected]>
Cc: "Rafael J. Wysocki" <[email protected]>
Cc: Zhang Rui <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>