powerpc/powernv: Support for OPAL console

This adds a udbg and an hvc console backend for supporting a console
using the OPAL console interfaces.

On OPAL v1 we have hvc0 mapped to whatever console the system was
configured for (network or hvsi serial port) via the service
processor.

On OPAL v2 we have hvcN mapped to the Nth console provided by OPAL
which generally corresponds to:

	hvc0 : network console (raw protocol)
	hvc1 : serial port S1 (hvsi)
	hvc2 : serial port S2 (hvsi)

Note: At this point, early debug console only works with OPAL v1
and shouldn't be enabled in a normal kernel.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
diff --git a/arch/powerpc/include/asm/opal.h b/arch/powerpc/include/asm/opal.h
index c7a3202..749de00 100644
--- a/arch/powerpc/include/asm/opal.h
+++ b/arch/powerpc/include/asm/opal.h
@@ -425,6 +425,11 @@
 extern int early_init_dt_scan_opal(unsigned long node, const char *uname,
 				   int depth, void *data);
 
+extern int opal_get_chars(uint32_t vtermno, char *buf, int count);
+extern int opal_put_chars(uint32_t vtermno, const char *buf, int total_len);
+
+extern void hvc_opal_init_early(void);
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* __OPAL_H */