[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>
diff --git a/arch/mips/txx9/rbtx4938/prom.c b/arch/mips/txx9/rbtx4938/prom.c
index ee18951..d73123c 100644
--- a/arch/mips/txx9/rbtx4938/prom.c
+++ b/arch/mips/txx9/rbtx4938/prom.c
@@ -22,4 +22,5 @@
 	prom_init_cmdline();
 #endif
 	add_memory_region(0, tx4938_get_mem_size(), BOOT_MEM_RAM);
+	txx9_sio_putchar_init(TX4938_SIO_REG(0) & 0xfffffffffULL);
 }