MIPS: Add 8250/16550 serial early printk driver

Signed-off-by: Yoichi Yuasa <yuasa@linux-mips.org>
Cc: linux-mips <linux-mips@linux-mips.org>
Patchwork: https://patchwork.linux-mips.org/patch/947/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

diff --cc arch/mips/Kconfig.debug
Simple merge

diff --cc arch/mips/include/asm/setup.h
Simple merge

diff --cc arch/mips/kernel/Makefile
Simple merge

diff --cc arch/mips/kernel/early_printk_8250.c
Simple merge