[MIPS] Cobalt: Move UART base definition to arch/mips/cobalt/console.c

They're only used in arch/mips/cobalt/console.c.

Signed-off-by: Yoichi Yuasa <yoichi_yuasa@tripeaks.co.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>