Many platforms support simple gateable clocks, fixed-rate clocks,
adjustable divider clocks and multi-parent multiplexer clocks.

This patch introduces basic clock types for the above-mentioned hardware
which share some common characteristics.

Based on original work by Jeremy Kerr and contribution by Jamie Iles.
Dividers and multiplexor clocks originally contributed by Richard Zhao &
Sascha Hauer.

Signed-off-by: Mike Turquette
Signed-off-by: Mike Turquette
Reviewed-by: Andrew Lunn
Tested-by: Andrew Lunn
Reviewed-by: Rob Herring
Cc: Russell King
Cc: Jeremy Kerr
Cc: Thomas Gleixner
Cc: Arnd Bergman
Cc: Paul Walmsley
Cc: Shawn Guo
Cc: Sascha Hauer
Cc: Jamie Iles
Cc: Richard Zhao
Cc: Saravana Kannan
Cc: Magnus Damm
Cc: Mark Brown
Cc: Linus Walleij
Cc: Stephen Boyd
Cc: Amit Kucheria
Cc: Deepak Saxena
Cc: Grant Likely
Signed-off-by: Arnd Bergmann