x86: Initial commit for running as a coreboot payload

Add a target for running u-boot as a coreboot payload in boards.cfg, a
board, CPU and a config. This is a skeleton implementation which always
reports the size of memory as 64 MB.

Signed-off-by: Gabe Black <gabeblack@chromium.org>
diff --git a/include/serial.h b/include/serial.h
index fbc1036..a298a0b 100644
--- a/include/serial.h
+++ b/include/serial.h
@@ -32,7 +32,7 @@
 	defined(CONFIG_MB86R0x) || defined(CONFIG_MPC5xxx) || \
 	defined(CONFIG_MPC83xx) || defined(CONFIG_MPC85xx) || \
 	defined(CONFIG_MPC86xx) || defined(CONFIG_SYS_SC520) || \
-	defined(CONFIG_TEGRA2)
+	defined(CONFIG_TEGRA2) || defined(CONFIG_SYS_COREBOOT)
 extern struct serial_device serial0_device;
 extern struct serial_device serial1_device;
 #if defined(CONFIG_SYS_NS16550_SERIAL)