Sometimes it is required to build only host U-Boot tools without building
U-Boot itself for either board.

For example:
 * In "buildroot" "uboot-tools" could be built for host just to have an ability
   to create uImage.
 * Linux distributions ship "mkimage" utility as a separate substance.

This patch allows building host U-Boot tools separately from U-Boot itself and
what is more important user only needs to have host compiler (gcc).

To build host tools just execute:
=====
make tools HOST_TOOLS_ONLY=yes
=====

Without this patch to generate tools user needs:
 1. Configure any existing board with "make XXX_config"
 2. Execute tools building but still cross-compiler will be invoked and if
    there's no proper cross-compiler in PATH compilation will fail.

Signed-off-by: Alexey Brodkin <abrodkin at synopsys.com>

Cc: Masahiro Yamada <yamada.m at jp.panasonic.com>
Cc: Tom Rini <trini at ti.com>
Cc: Simon Glass <sjg at chromium.org>

--- u-boot-2014.07.orig/Kbuild	2014-07-14 19:16:45.000000000 +0200
+++ u-boot-2014.07/Kbuild	2014-08-11 10:06:13.311946939 +0200
@@ -4,6 +4,9 @@
 # 1) Generate generic-asm-offsets.h
 # 2) Generate asm-offsets.h
 
+# Don't execute target below if building host tools only
+ifneq ($(HOST_TOOLS_ONLY),yes)
+
 #####
 # 1) Generate generic-asm-offsets.h
 
@@ -85,3 +88,5 @@ arch/$(ARCH)/lib/asm-offsets.s: arch/$(A
 
 $(obj)/$(offsets-file): arch/$(ARCH)/lib/asm-offsets.s Kbuild
 	$(call cmd,offsets)
+
+endif