kbuild: change out-of-tree build

This commit changes the working directory
where the build process occurs.

Before this commit, build process occurred under the source
tree for both in-tree and out-of-tree build.

That's why we needed to add $(obj) prefix to all generated
files in makefiles like follows:
  $(obj)u-boot.bin:  $(obj)u-boot

Here, $(obj) is empty for in-tree build, whereas it points
to the output directory for out-of-tree build.

And our old build system changes the current working directory
with "make -C <sub-dir>" syntax when descending into the
sub-directories.

On the other hand, Kbuild uses a different idea
to handle out-of-tree build and directory descending.

The build process of Kbuild always occurs under the output tree.
When "O=dir/to/store/output/files" is given, the build system
changes the current working directory to that directory and
restarts the make.

Kbuild uses "make -f $(srctree)/scripts/Makefile.build obj=<sub-dir>"
syntax for descending into sub-directories.
(We can write it like "make $(obj)=<sub-dir>" with a shorthand.)
This means the current working directory is always the top
of the output directory.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Tested-by: Gerhard Sittig <gsi@denx.de>
diff --git a/tools/Makefile b/tools/Makefile
index 21341b7..9b19dcb 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -142,8 +142,8 @@
 always := $(hostprogs-y)
 
 # Generated LCD/video logo
-LOGO_H = $(OBJTREE)/include/bmp_logo.h
-LOGO_DATA_H = $(OBJTREE)/include/bmp_logo_data.h
+LOGO_H = $(objtree)/include/bmp_logo.h
+LOGO_DATA_H = $(objtree)/include/bmp_logo_data.h
 LOGO-$(CONFIG_LCD_LOGO) += $(LOGO_H)
 LOGO-$(CONFIG_LCD_LOGO) += $(LOGO_DATA_H)
 LOGO-$(CONFIG_VIDEO_LOGO) += $(LOGO_H)
@@ -151,14 +151,14 @@
 
 # Generic logo
 ifeq ($(LOGO_BMP),)
-LOGO_BMP= logos/denx.bmp
+LOGO_BMP= $(srctree)/$(src)/logos/denx.bmp
 
 # Use board logo and fallback to vendor
 ifneq ($(wildcard logos/$(BOARD).bmp),)
-LOGO_BMP= logos/$(BOARD).bmp
+LOGO_BMP= $(srctree)/$(src)/logos/$(BOARD).bmp
 else
 ifneq ($(wildcard logos/$(VENDOR).bmp),)
-LOGO_BMP= logos/$(VENDOR).bmp
+LOGO_BMP= $(srctree)/$(src)/logos/$(VENDOR).bmp
 endif
 endif
 
@@ -187,8 +187,8 @@
 
 subdir-y := kernel-doc
 
-$(LOGO_H):	$(obj)bmp_logo $(LOGO_BMP)
-	$(obj)./bmp_logo --gen-info $(LOGO_BMP) > $@
+$(LOGO_H):	$(obj)/bmp_logo $(LOGO_BMP)
+	$(obj)/bmp_logo --gen-info $(LOGO_BMP) > $@
 
-$(LOGO_DATA_H):	$(obj)bmp_logo $(LOGO_BMP)
-	$(obj)./bmp_logo --gen-data $(LOGO_BMP) > $@
+$(LOGO_DATA_H):	$(obj)/bmp_logo $(LOGO_BMP)
+	$(obj)/bmp_logo --gen-data $(LOGO_BMP) > $@