IASL compiler does not provide a command line option to turn off
its non-warning message. To quieten the output when 'make -s',
redirect its output to /dev/null.
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
 quiet_cmd_acpi_c_asl= ASL     $<
 cmd_acpi_c_asl=         \
        $(CPP) -x assembler-with-cpp -P $(UBOOTINCLUDE) -o $<.tmp $<; \
-       iasl -p $< -tc $<.tmp; \
+       iasl -p $< -tc $<.tmp $(if $(KBUILD_VERBOSE:1=), >/dev/null); \
        mv $(patsubst %.asl,%.hex,$<) $@
 
 $(obj)/dsdt.c:    $(src)/dsdt.asl