[MIPS] TXx9: Support early_printk

Kill jmr3927-specific prom_putchar and add txx9-generic prom_putchar
to support early_printk.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
6 files changed