AMD/bettong: Add UART support

The function delay in uart8250mem.c is not enough for hudson. I guess
there are some problems in lapic_timer(). I uploaded a patch to gerrit
to show the way to enable UART feature.
http://review.coreboot.org/#/c/12343/4

Currently the HUDSON_UART is unchecked by default. Select HUDSON_UART to
enable this feature.

The UART is test at BIOS stage.

Since it is not a standart UART device, the windows internal UART driver
doesnt support it. I guess we need a driver to use it on windows.

Change-Id: I4cec833cc2ff8069c82886837f7cbd4483ff11bb
Signed-off-by: Zheng Bao <zheng.bao@amd.com>
Signed-off-by: Zheng Bao <fishbaozi@gmail.com>
Reviewed-on: http://review.coreboot.org/11749
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
diff --git a/src/southbridge/amd/pi/hudson/hudson.h b/src/southbridge/amd/pi/hudson/hudson.h
index 6f37c90..23d9b31 100644
--- a/src/southbridge/amd/pi/hudson/hudson.h
+++ b/src/southbridge/amd/pi/hudson/hudson.h
@@ -112,6 +112,9 @@
 
 int s3_save_nvram_early(u32 dword, int size, int  nvram_pos);
 int s3_load_nvram_early(int size, u32 *old_dword, int nvram_pos);
+#if IS_ENABLED(CONFIG_HUDSON_UART)
+void configure_hudson_uart(void);
+#endif
 
 #else
 void hudson_enable(device_t dev);