efi: Add a serial driver

Add a serial driver which makes use of EFI's console in/out service.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested on Intel Crown Bay and QEMU
Tested-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig
index 078246d..b5a91b7 100644
--- a/drivers/serial/Kconfig
+++ b/drivers/serial/Kconfig
@@ -44,6 +44,15 @@
 	  will need to provide parameters to make this work. The driver will
 	  be available until the real driver model serial is running.
 
+config DEBUG_EFI_CONSOLE
+	bool "EFI"
+	depends on EFI_APP
+	help
+	  Select this to enable a debug console which calls back to EFI to
+	  output to the console. This can be useful for early debugging of
+	  U-Boot when running on top of EFI (Extensive Firmware Interface).
+	  This is a type of BIOS used by PCs.
+
 endchoice
 
 config DEBUG_UART_BASE