cpu/arm/k60: Removed custom C compile rules.

No reason to have custom rules when they are not different from the
default rules in Makefile.include.

The original Makefile.include rules are even better because they handle
dependency generation better.

Added missing CUSTOM_RULE_LINK to Makefile.k60 as well.

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
cpu/arm/k60: Move platform specific upload commands.

Moved Mulle specific commands to platform/mulle/Makefile.mulle

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