cpu/arm/k60: Add driver for on-CPU ADC.

The driver provides functions for reading the raw measurement as well
as calibration, however, no initialization is provided and must be
performed before calling any of the functions.

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
platform/mulle: Add voltage reading API.

A couple of helper functions to configure and read the onboard VBAT and
VCHR voltages. The ADC channels as well as the reference voltages can
be configured via config-board.h in the platform/mulle directory.

TODO: Make voltage_init() obey configuration (remove hard-coded channels etc.)

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
examples/mulle-voltages: Simple voltage reader for Mulle platform.

A basic example showing how to use the voltage reader functions on the
Mulle platform.

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
platform/mulle: Add missing 'extern' to rf230bb.h

An accidental double definition of the struct rf230_driver caused
problems when building with -fno-common

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
cpu/arm/k60: Change default debug level to -g3

Added a few comments about the debugging options in CFLAGS in the
cpu Makefile.

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
cpu/arm/k60: Add -fno-common to CFLAGS.

-fno-common avoids accidentally using the same variable in different
files by disabling common symbols.

When a variable is supposed to be used from multiple files it should be
declared extern in the header file and only have one definition (in a
.c-file), with or without an initial value.

See also:
 - https://gcc.gnu.org/onlinedocs/gcc/Code-Gen-Options.html
 - http://permalink.gmane.org/gmane.comp.gcc.help/41650

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
cpu/arm/k60: Clean up warnings in 1-wire driver.

- Corrects a few missing type casts which were not caught before.
- Add missing declaration of ow_skip_or_match_rom() to onewire.h.

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
platform/mulle: Fix compiler warning in flash.c.

Add missing const keyword to pointer to write queue buffer.

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
cpu/arm/k60: Remove old asm startcode.

This is a leftover since e673da1 cpu/arm/k60: Use C startup instead of ASM.

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
cpu/arm/k60: Add .ramcode handling to startup code.

Use __attribute__((section (".ramcode"))) to place code in RAM if
needed.

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
Fixed radio interrupt routine name.
low power.