cpu/rl78/ST7579: Fix Warnings and allow platform to decide build

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
cpu/rl78/Makefile.rl78: CONTIKI_SOURCEFILES: Platform make should include this

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
platform/yrdkrl78-g14/Makefile.yrdkrl78-g14: Build ADF7242 and ST7579

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
platform/eval-adf7xxxmb4z: Fix build errors

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
cpu/rl78/adf7242/adf7242: Restore nl after func (no functional changes)

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>