acpi: Allow include files within the board directory

Some .asl files include others using the iasl 'include' directive. This
needs to be able to find the files referenced.

For an out-of-tree build the source directory is not the current
directory. Moreover, U-Boot preprocesses the input file and puts the
result in the output directory. So iasl does not know where the real
source file came from.

Add a -I option to produce the correct behaviour. We could add an option
to not preprocess the .asl source, but for now that seems unnecessary.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 77ad282..3de78d9 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -461,7 +461,8 @@
 cmd_acpi_c_asl=         \
 	$(CPP) -x assembler-with-cpp -D__ASSEMBLY__ -D__ACPI__ \
 		-P $(UBOOTINCLUDE) -o $(ASL_TMP) $< && \
-	iasl -p $@ -tc $(ASL_TMP) $(if $(KBUILD_VERBOSE:1=), >/dev/null) && \
+	iasl -p $@ -I $(srctree)/board/$(BOARDDIR) -tc $(ASL_TMP) \
+		$(if $(KBUILD_VERBOSE:1=), >/dev/null) && \
 	mv $(patsubst %.c,%.hex,$@) $@
 
 $(obj)/dsdt.c:    $(src)/dsdt.asl