[POWERPC] Enable the RTAS udbg console on IBM Cell Blade

Enable the RTAS udbg console on IBM Cell Blade, this allows xmon
to work.
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/Kconfig

@@ -419,6 +419,7 @@ config PPC_IBM_CELL_BLADE
 	select PPC_RTAS
 	select MMIO_NVRAM
 	select PPC_UDBG_16550
+	select UDBG_RTAS_CONSOLE
 
 config UDBG_RTAS_CONSOLE
 	bool

arch/powerpc/platforms/cell/setup.c

@@ -141,6 +141,10 @@ static int __init cell_probe(void)
 	    !of_flat_dt_is_compatible(root, "IBM,CPBW-1.0"))
 		return 0;
 
+#ifdef CONFIG_UDBG_RTAS_CONSOLE
+	udbg_init_rtas_console();
+#endif
+
 	hpte_init_native();
 
 	return 1;