Blackfin: allow serial console to be disabled

Some devices have no UART device pulled out, so allow people to disable the
driver completely in favor of other methods (like JTAG-console).

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/cpu/blackfin/serial.c b/cpu/blackfin/serial.c
index 0d6f377..42534bd 100644
--- a/cpu/blackfin/serial.c
+++ b/cpu/blackfin/serial.c
@@ -29,6 +29,8 @@
 #include <asm/blackfin.h>
 #include <asm/mach-common/bits/uart.h>
 
+#ifdef CONFIG_UART_CONSOLE
+
 #if defined(UART_LSR) && (CONFIG_UART_CONSOLE != 0)
 # error CONFIG_UART_CONSOLE must be 0 on parts with only one UART
 #endif
@@ -170,3 +172,5 @@
 	while (*s)
 		serial_putc(*s++);
 }
+
+#endif
diff --git a/cpu/blackfin/serial.h b/cpu/blackfin/serial.h
index 90fceec..f671096 100644
--- a/cpu/blackfin/serial.h
+++ b/cpu/blackfin/serial.h
@@ -14,6 +14,10 @@
 #include <asm/blackfin.h>
 #include <asm/mach-common/bits/uart.h>
 
+#ifndef CONFIG_UART_CONSOLE
+# define CONFIG_UART_CONSOLE 0
+#endif
+
 #ifdef CONFIG_DEBUG_EARLY_SERIAL
 # define BFIN_DEBUG_EARLY_SERIAL 1
 #else