MIPS: EMMA: Kconfig reorganization

- Move EMMA related stuff into arch/mips/emma/Kconfig
- Create CONFIG_SOC_EMMA* to handle more EMMA SoCs effectively
- Rename CONFIG_MARKEINS into CONFIG_NEC_MARKEINS

Signed-off-by: Shinya Kuribayashi <shinya.kuribayashi@necel.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>