intel/lynxpoint: Make inclusion of Intel ME optional

Current build configuration always wants to include an Intel Management Engine
(ME) firmware (`me.bin`) on Intel Lynx Point systems.  However, we can have a
working coreboot without it, as long as the factory delivered ME firmware is
kept untouched in the flash ROM. So let the user decide if a ME firmware will
be included in the build by introducing the Kconfig option `HAVE_ME_BIN`.

The same was done in commit 99fd30e4 (sandybridge: Make inclusion of me.bin
optional) [1] for Intel Sandy Bridge (BD82x6x).

[1] http://review.coreboot.org/3522

Change-Id: I7c6048fd0f56288769ad90acbfb67b908ac8d824
Signed-off-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-on: http://review.coreboot.org/6047
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>

src/southbridge/intel/lynxpoint/Kconfig

@@ -100,8 +100,20 @@ config IFD_BIN_PATH
 	depends on !BUILD_WITH_FAKE_IFD
 	default "3rdparty/mainboard/$(MAINBOARDDIR)/descriptor.bin"
 
+config HAVE_ME_BIN
+	bool "Add Intel Management Engine firmware"
+	default y
+	help
+	  The Intel processor in the selected system requires a special firmware
+	  for an integrated controller called Management Engine (ME). The ME
+	  firmware might be provided in coreboot's 3rdparty repository. If
+	  not and if you don't have the firmware elsewhere, you can still
+	  build coreboot without it. In this case however, you'll have to make
+	  sure that you don't overwrite your ME firmware on your flash ROM.
+
 config ME_BIN_PATH
 	string "Path to management engine firmware"
+	depends on HAVE_ME_BIN
 	default "3rdparty/mainboard/$(MAINBOARDDIR)/me.bin"
 
 config IFD_BIN_PATH

src/southbridge/intel/lynxpoint/Makefile.inc

@@ -85,11 +85,13 @@ endif
 	printf "    DD         Adding Intel Firmware Descriptor\n"
 	dd if=$(IFD_BIN_PATH) \
 		of=$(obj)/coreboot.pre conv=notrunc >/dev/null 2>&1
+ifeq ($(CONFIG_HAVE_ME_BIN),y)
 	printf "    IFDTOOL    me.bin -> coreboot.pre\n"
 	$(objutil)/ifdtool/ifdtool \
 		-i ME:$(CONFIG_ME_BIN_PATH) \
 		$(obj)/coreboot.pre
 	mv $(obj)/coreboot.pre.new $(obj)/coreboot.pre
+endif
 ifeq ($(CONFIG_LOCK_MANAGEMENT_ENGINE),y)
 	printf "    IFDTOOL    Locking Management Engine\n"
 	$(objutil)/ifdtool/ifdtool -l $(obj)/coreboot.pre