x86: Add generic EFI payload support

It is possible to create a generic EFI payload for all x86 boards.
The payload is configured to include as many generic drivers as
possible. All stuff that touches low-level initialization are not
allowed as such is the EFI BIOS's responsibility. Platform specific
drivers (like gpio, spi, etc) are not included.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/board/efi/Kconfig b/board/efi/Kconfig
index 6f86a48..d37f6ff 100644
--- a/board/efi/Kconfig
+++ b/board/efi/Kconfig
@@ -12,8 +12,17 @@
 	  takes over once the RAM, video and CPU are fully running.
 	  U-Boot is loaded as an application from EFI.
 
+config TARGET_EFI_PAYLOAD
+	bool "efi payload"
+	help
+	  This target is used for running U-Boot on top of EFI. In
+	  this case EFI does the early initialisation, and U-Boot
+	  takes over once the RAM, video and CPU are fully running.
+	  U-Boot is loaded as a payload from EFI.
+
 endchoice
 
 source "board/efi/efi-x86/Kconfig"
+source "board/efi/efi-x86_payload/Kconfig"
 
 endif