m68k: merge compile flags -ffixed-d7 -sep-data

All arch/m68k/cpu/*/config.mk define the same flags
  PLAGFORM_REFLFLAGS += -ffixed-d7 -msep-data
Move it to arch/m68k/config.mk

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Jason Jin <Jason.jin@freescale.com>
7 files changed