x86: efi: Add room for the binman definition in the dtb

At present only 4KB of spare space is left in the DTB when building the
EFI app. Increase this to 32KB so there is plenty of space to insert the
binman definition. This cannot be expanded later (as with OF_SEPARATE)
because the ELF image has already been built.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviwed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/arch/x86/dts/Makefile b/arch/x86/dts/Makefile
index be209aa..5c8c05e 100644
--- a/arch/x86/dts/Makefile
+++ b/arch/x86/dts/Makefile
@@ -24,7 +24,7 @@
 
 targets += $(dtb-y)
 
-DTC_FLAGS += -R 4 -p 0x1000
+DTC_FLAGS += -R 4 -p $(if $(CONFIG_EFI_APP),0x8000,0x1000)
 
 PHONY += dtbs
 dtbs: $(addprefix $(obj)/, $(dtb-y))