platform/mulle/power-control: New power control API.

The power-control API provides simple wrappers to turn on and off
auxiliary power on the Mulle board.

The auxiliary power lines currently controlled by this library are:
- Vperiph
- Vsec
- Analog VDD

Vperiph is only used for onboard peripherals while AVDD and VSEC are
available in the expansion port.

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
platform/mulle: Use power-control API in LIS3DH driver.

This patch replaces the explicit GPIO writes with power
control library calls to turn on Vperiph during LIS3DH
initialization.

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
platform/mulle/power-control: Move board definitions into separate file.

power-control-board.h now contains all the hardware specific register names
and addresses.
power-control.h only contains the function declarations.

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>