hw: mcu: kinetis: k8x: fix flash write alignment
hw: mcu: kinetis: k8x: fix flash write alignment

Flash in Kinetis devices has either 4 or 8 byte write alignment,
depending on the specific model. For K8x this is 4 bytes so fix the
current syscfg.

Signed-off-by: Fabio Utzig <66676b1ceaf93296e098708c09494361103aa635@apache.org>

mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core