platform/mulle: Make hal_spi_{send,receive} static inline.

Causes problems when linking with Clang.

See also: http://clang.llvm.org/compatibility.html#inline

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
cpu/arm/k60: Add include guard to K60.h

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