regmap: port regmap_update_bits from linux ...

Port the regmap_update_bits function from linux v4.14-rc1 to barebox.

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

regmap: Add regmap_write_bits() function ...

Add code implementing a simple version of regmap_write_bits().

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

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>