kbuild: add dummy obj-y to create built-in.o

We are going to switch over to Kbuild in upcoming commits.

Each makefile must have non-empty obj- or obj-y
to generate built-in.o on Kbuild.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/board/freescale/common/Makefile b/board/freescale/common/Makefile
index 25f063d..f6a0879 100644
--- a/board/freescale/common/Makefile
+++ b/board/freescale/common/Makefile
@@ -13,7 +13,10 @@
 endif
 endif
 
-ifndef MINIMAL
+ifdef MINIMAL
+# necessary to create built-in.o
+obj- := __dummy__.o
+else
 obj-$(CONFIG_FSL_CADMUS)	+= cadmus.o
 obj-$(CONFIG_FSL_VIA)		+= cds_via.o
 obj-$(CONFIG_FMAN_ENET)	+= fman.o
diff --git a/board/samsung/origen/Makefile b/board/samsung/origen/Makefile
index 37acba7..1add9fe 100644
--- a/board/samsung/origen/Makefile
+++ b/board/samsung/origen/Makefile
@@ -5,6 +5,9 @@
 #
 
 ifdef CONFIG_SPL_BUILD
+# necessary to create built-in.o
+obj- := __dummy__.o
+
 hostprogs-y := tools/mkorigenspl
 always := $(hostprogs-y)
 
diff --git a/board/samsung/smdkv310/Makefile b/board/samsung/smdkv310/Makefile
index 9e37b4e..de0da16 100644
--- a/board/samsung/smdkv310/Makefile
+++ b/board/samsung/smdkv310/Makefile
@@ -5,6 +5,9 @@
 #
 
 ifdef CONFIG_SPL_BUILD
+# necessary to create built-in.o
+obj- := __dummy__.o
+
 hostprogs-y := tools/mksmdkv310spl
 always := $(hostprogs-y)
 else
diff --git a/board/spear/common/Makefile b/board/spear/common/Makefile
index 08dc09f..b0ba320 100644
--- a/board/spear/common/Makefile
+++ b/board/spear/common/Makefile
@@ -5,7 +5,10 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-ifndef CONFIG_SPL_BUILD
+ifdef CONFIG_SPL_BUILD
+# necessary to create built-in.o
+obj- := __dummy__.o
+else
 obj-y	:= spr_misc.o
 obj-y	+= spr_lowlevel_init.o
 endif
diff --git a/board/spear/x600/Makefile b/board/spear/x600/Makefile
index f9053fe..18d3dd2 100644
--- a/board/spear/x600/Makefile
+++ b/board/spear/x600/Makefile
@@ -5,6 +5,9 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-ifndef CONFIG_SPL_BUILD
+ifdef CONFIG_SPL_BUILD
+# necessary to create built-in.o
+obj- := __dummy__.o
+else
 obj-y	:= fpga.o x600.o
 endif