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>