Merge tag 'tags/linear-ranges-lib' into psy-next

lib: Add linear ranges helper library and start using it

Series extracts a "linear ranges" helper out of the regulator
framework. Linear ranges helper is intended to help converting
real-world values to register values when conversion is linear. I
suspect this is useful also for power subsystem and possibly for clk.

Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>