env: Provide a work-around for unquoting fdtfile

Some boards use a CONFIG option to specify the value of this variable.
This is normally handled by efi_get_distro_fdt_name() but in the case
of sunxi this does not work, since 'soc' is sunxi, but the files are
in the allwinner directory.

Provide a work-around for this particular case.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/Makefile b/Makefile
index 5f90cea..b1aba35 100644
--- a/Makefile
+++ b/Makefile
@@ -1864,6 +1864,7 @@
 		$(CPP) -P $(cpp_flags) -x assembler-with-cpp -undef \
 			-D__ASSEMBLY__ \
 			-D__UBOOT_CONFIG__ \
+			-DDEFAULT_DEVICE_TREE=$(subst ",,$(CONFIG_DEFAULT_DEVICE_TREE)) \
 			-I . -I include -I $(srctree)/include \
 			-include linux/kconfig.h -include include/config.h \
 			-I$(srctree)/arch/$(ARCH)/include \