Makefile: Tidy up SPL dtb production

Use the SPL_NAME variable to simplify the rules. Drop the SPL targets
clean-files since the SPL and TPL dts/ directories are removed by
existing rules. Move the SPL rules into a new spl_dtbs to avoid the
complicated $(if) construct.

Also drop unused pieces from the 'targets' variable.

With this, SPL and TPL have separate dtbs which respect the various
u-boot,dm-spl / u-boot,dm-tpl tags.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/dts/Makefile b/dts/Makefile
index c0a953f..94967cf 100644
--- a/dts/Makefile
+++ b/dts/Makefile
@@ -16,13 +16,10 @@
 DTB := arch/$(ARCH)/dts/$(DEVICE_TREE).dtb
 endif
 
-spl/$(obj)/dt-spl.dtb: $(DTB) $(objtree)/tools/fdtgrep FORCE
+$(obj)/dt-$(SPL_NAME).dtb: dts/dt.dtb $(objtree)/tools/fdtgrep FORCE
 	mkdir -p $(dir $@)
 	$(call if_changed,fdtgrep)
 
-tpl/$(obj)/dt-tpl.dtb: $(DTB) $(objtree)/tools/fdtgrep FORCE
-	$(call if_changed,fdtgrep)
-
 ifeq ($(CONFIG_OF_DTB_PROPS_REMOVE),y)
 $(obj)/dt.dtb: $(DTB) $(objtree)/tools/fdtgrep FORCE
 	$(call if_changed,fdt_rm_props)
@@ -31,7 +28,7 @@
 	$(call if_changed,shipped)
 endif
 
-targets += dt.dtb dt-spl.dtb dt-tpl.dtb
+targets += dt.dtb
 
 $(DTB): arch-dtbs
 	$(Q)test -e $@ || (						\
@@ -55,12 +52,15 @@
 obj-$(CONFIG_OF_EMBED) := dt.dtb.o
 endif
 
-dtbs: $(obj)/dt.dtb \
-		$(if $(CONFIG_SPL),spl/$(obj)/dt-spl.dtb) \
-		$(if $(CONFIG_TPL),tpl/$(obj)/dt-tpl.dtb)
+# Target for U-Boot proper
+dtbs: $(obj)/dt.dtb
 	@:
 
-clean-files := dt.dtb.S dt-spl.dtb.S dt-tpl.dtb.S
+# Target for SPL/TPL
+spl_dtbs: $(obj)/dt-$(SPL_NAME).dtb
+	@:
+
+clean-files := dt.dtb.S
 
 # Let clean descend into dts directories
 subdir- += ../arch/arm/dts ../arch/microblaze/dts ../arch/mips/dts ../arch/sandbox/dts ../arch/x86/dts ../arch/powerpc/dts ../arch/riscv/dts
diff --git a/scripts/Makefile.spl b/scripts/Makefile.spl
index e83e93e..c929638 100644
--- a/scripts/Makefile.spl
+++ b/scripts/Makefile.spl
@@ -37,6 +37,8 @@
 SPL_NAME := spl
 endif
 
+export SPL_NAME
+
 ifdef CONFIG_SPL_BUILD
 SPL_ := SPL_
 ifeq ($(CONFIG_TPL_BUILD),y)
@@ -459,9 +461,8 @@
 PHONY += FORCE
 FORCE:
 
-PHONY += dtbs
-dtbs:
-	$(Q)$(MAKE) $(build)=dts dtbs
+$(obj)/dts/dt-$(SPL_NAME).dtb: dts/dt.dtb
+	$(Q)$(MAKE) $(build)=$(obj)/dts spl_dtbs
 
 # Declare the contents of the .PHONY variable as phony.  We keep that
 # information in a variable so we can use it in if_changed and friends.