kconfig: add board Kconfig and defconfig files

This commit adds:
 - arch/${ARCH}/Kconfig
    provide a menu to select target boards
 - board/${VENDOR}/${BOARD}/Kconfig or board/${BOARD}/Kconfig
    set CONFIG macros to the appropriate values for each board
 - configs/${TARGET_BOARD}_defconfig
    default setting of each board

(This commit was automatically generated by a conversion script
based on boards.cfg)

In Linux Kernel, defconfig files are located under
arch/${ARCH}/configs/ directory.
It works in Linux Kernel since ARCH is always given from the
command line for cross compile.

But in U-Boot, ARCH is not given from the command line.
Which means we cannot know ARCH until the board configuration is done.
That is why all the "*_defconfig" files should be gathered into a
single directory ./configs/.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Acked-by: Simon Glass <sjg@chromium.org>

arch/microblaze/Kconfig

@@ -0,0 +1,18 @@
+menu "MicroBlaze architecture"
+	depends on MICROBLAZE
+
+config SYS_ARCH
+	string
+	default "microblaze"
+
+choice
+	prompt "Target select"
+
+config TARGET_MICROBLAZE_GENERIC
+	bool "Support microblaze-generic"
+
+endchoice
+
+source "board/xilinx/microblaze-generic/Kconfig"
+
+endmenu