platform/mulle: Make lis3dh spi_transfer static.

Hides it from other compilation units.

TODO: Consolidate all spi_transfer-like functions into one.

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
platform/mulle: Clean up flash driver.

- Replaced subsequent calls to spi_write+spi_read with spi_transfer.
- Cleaned up type names.

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
platform/mulle: Print CPUID on bootup.

Helpful for debugging problems with the wrong CPU revision.

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