acpi: Don't build SSDT files on every build; store them in git

The SSDT files are rarely modified - recent QEMU versions don't use
them at all and adding features to them in SeaBIOS has been
deprecated.  It no longer makes sense to generate them on every build.
The content will remain (for use on old machine types in QEMU) in
static files committed to the SeaBIOS git repo.  If the contents do
need to be generated a new build target (make iasl) is available.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
diff --git a/Makefile b/Makefile
index 6f1bb68..cbe9454 100644
--- a/Makefile
+++ b/Makefile
@@ -248,7 +248,7 @@
 iasl-option=$(shell if test -z "`$(1) $(2) 2>&1 > /dev/null`" \
     ; then echo "$(2)"; else echo "$(3)"; fi ;)
 
-$(OUT)%.hex: %.dsl ./scripts/acpi_extract_preprocess.py ./scripts/acpi_extract.py
+%.hex: %.dsl ./scripts/acpi_extract_preprocess.py ./scripts/acpi_extract.py
 	@echo "  Compiling IASL $@"
 	$(Q)$(CPP) $(CPPFLAGS) $< -o $(OUT)$*.dsl.i.orig
 	$(Q)$(PYTHON) ./scripts/acpi_extract_preprocess.py $(OUT)$*.dsl.i.orig > $(OUT)$*.dsl.i
@@ -256,7 +256,7 @@
 	$(Q)$(PYTHON) ./scripts/acpi_extract.py $(OUT)$*.lst > $(OUT)$*.off
 	$(Q)cat $(OUT)$*.off > $@
 
-$(OUT)src/fw/acpi.o: $(OUT)src/fw/acpi-dsdt.hex $(OUT)src/fw/ssdt-proc.hex $(OUT)src/fw/ssdt-pcihp.hex $(OUT)src/fw/ssdt-misc.hex
+iasl: src/fw/acpi-dsdt.hex src/fw/ssdt-proc.hex src/fw/ssdt-pcihp.hex src/fw/ssdt-misc.hex
 
 ################ Kconfig rules