[RFC PATCH] powerpc: udbg: export udbg_putc

In a randconfig with CONFIG_SERIAL_CPM=m and
CONFIG_PPC_EARLY_DEBUG_CPM=y, there is a build error:
ERROR: modpost: "udbg_putc" [drivers/tty/serial/cpm_uart/cpm_uart.ko] undefined!

The build can be fixed by exporting "udbg_putc" in udbg.c.

OTOH, maybe something like this is more appropriate in
arch/powerpc/Kconfig.debug?

config PPC_EARLY_DEBUG_CPM
	bool "Early serial debugging for Freescale CPM-based serial ports"
-	depends on SERIAL_CPM
+	depends on SERIAL_CPM=y

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Christophe Leroy <redacted>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: "Pali Rohár" <pali@kernel.org>
---
 arch/powerpc/kernel/udbg.c |    1 +
 1 file changed, 1 insertion(+)

diff -- a/arch/powerpc/kernel/udbg.c b/arch/powerpc/kernel/udbg.c

--- a/arch/powerpc/kernel/udbg.c
+++ b/arch/powerpc/kernel/udbg.c

@@ -14,6 +14,7 @@
 #include <asm/udbg.h>
 
 void (*udbg_putc)(char c);
+EXPORT_SYMBOL(udbg_putc);
 void (*udbg_flush)(void);
 int (*udbg_getc)(void);
 int (*udbg_getc_poll)(void);