kconfig: switch to Kconfig

This commit enables Kconfig.
Going forward, we use Kconfig for the board configuration.
mkconfig will never be used. Nor will include/config.mk be generated.

Kconfig must be adjusted for U-Boot because our situation is
a little more complicated than Linux Kernel.
We have to generate multiple boot images (Normal, SPL, TPL)
from one source tree.
Each image needs its own configuration input.

Usage:

Run "make <board>_defconfig" to do the board configuration.

It will create the .config file and additionally spl/.config, tpl/.config
if SPL, TPL is enabled, respectively.

You can use "make config", "make menuconfig" etc. to create
a new .config or modify the existing one.

Use "make spl/config", "make spl/menuconfig" etc. for spl/.config
and do likewise for tpl/.config file.

The generic syntax of configuration targets for SPL, TPL is:

  <target_image>/<config_command>

Here, <target_image> is either 'spl' or 'tpl'
      <config_command> is 'config', 'menuconfig', 'xconfig', etc.

When the configuration is done, run "make".
(Or "make <board>_defconfig all" will do the configuration and build
in one time.)

For futher information of how Kconfig works in U-Boot,
please read the comment block of scripts/multiconfig.py.

By the way, there is another item worth remarking here:
coexistence of Kconfig and board herder files.

Prior to Kconfig, we used C headers to define a set of configs.

We expect a very long term to migrate from C headers to Kconfig.
Two different infractructure must coexist in the interim.

In our former configuration scheme, include/autoconf.mk was generated
for use in makefiles.
It is still generated under include/, spl/include/, tpl/include/ directory
for the Normal, SPL, TPL image, respectively.

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

scripts/Makefile.build

@@ -3,14 +3,14 @@
 # ==========================================================================
 
 # Modified for U-Boot
-ifeq ($(CONFIG_TPL_BUILD),y)
-  src := $(patsubst tpl/%,%,$(obj))
-else
-  ifeq ($(CONFIG_SPL_BUILD),y)
-    src := $(patsubst spl/%,%,$(obj))
-  else
-    src := $(obj)
-  endif
+prefix := tpl
+src := $(patsubst $(prefix)/%,%,$(obj))
+ifeq ($(obj),$(src))
+prefix := spl
+src := $(patsubst $(prefix)/%,%,$(obj))
+ifeq ($(obj),$(src))
+prefix := .
+endif
 endif
 
 PHONY := __build
@@ -40,18 +40,9 @@ subdir-asflags-y :=
 subdir-ccflags-y :=
 
 # Read auto.conf if it exists, otherwise ignore
--include include/config/auto.conf
-
-# Added for U-Boot: Load U-Boot configuration
-ifeq ($(CONFIG_TPL_BUILD),y)
-  -include include/tpl-autoconf.mk
-else
-  ifeq ($(CONFIG_SPL_BUILD),y)
-    -include include/spl-autoconf.mk
-  else
-    -include include/autoconf.mk
-  endif
-endif
+# Modified for U-Boot
+-include $(prefix)/include/config/auto.conf
+-include $(prefix)/include/autoconf.mk
 
 include scripts/Kbuild.include