regmap: Add missing prototype for regmap_exit() ...

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Add initial regmap support ...

This adds initial regmap support. Function prototypes are from
the Kernel, the implemention is mostly rewritten. Currently the
regmap support is limited to the bare minimum to get started.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>