Fixed implicit function declaration warnings.
platform/mulle: Add missing include.

Added string.h for strlen().

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
cpu/arm/k60: Fix compiler warnings in power-modes.c

False warnings about unused variables when doing dummy reads from
power control register:

warning: variable ‘dummy’ set but not used [-Wunused-but-set-variable]

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
platform/mulle: Add softfloat CFLAGS.

Added -msoft-float and -mfloat-abi=soft to CFLAGS. This fixes an issue
where the default float ABI was defined as hard float.

This fixes #10 Clang generates hardfloat instructions on Mulle

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