MIPS: Lantiq: Add NOR flash support

This patch adds the driver/map for NOR devices attached to the SoC via the
External Bus Unit (EBU).

Signed-off-by: John Crispin <blogic@openwrt.org>
Signed-off-by: Ralph Hempel <ralph.hempel@lantiq.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Daniel Schwierzeck <daniel.schwierzeck@googlemail.com>
Cc: linux-mips@linux-mips.org
Cc: linux-mtd@lists.infradead.org
Acked-by: Artem Bityutskiy <dedekind1@gmail.com>
Patchwork: https://patchwork.linux-mips.org/patch/2285/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>