android: gallium/aux: update old generated sources rules

This is in preparation for additional generated sources rules for Android
which will require ad hoc rules, so it is necessary to replace old ones

NOTE: pre-existing gen rules based on $(transform-generated-source) macro
are both obsolete and use of '%' pattern rule is incompatible with ad hoc
python commands for different targets

Changelog:
- remove util/u_format_srgb.c target
- replace obsolete indices/{u_indices,unfilled}_gen.c 'common' gen rules
  with 'per target' gen rules using $(MESA_PYTHON3) as per meson gen rules

Fixes: 3471af9c6c ("gallium/aux: Add GPU tracepoint mechanism")
Acked-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7942>

src/gallium/auxiliary/Android.mk

@@ -64,13 +64,19 @@ LOCAL_MODULE_CLASS := STATIC_LIBRARIES
 intermediates := $(call local-generated-sources-dir)
 LOCAL_GENERATED_SOURCES := $(addprefix $(intermediates)/, $(GENERATED_SOURCES))
 
-$(LOCAL_GENERATED_SOURCES): PRIVATE_PYTHON := $(MESA_PYTHON2)
-$(LOCAL_GENERATED_SOURCES): PRIVATE_CUSTOM_TOOL = $(PRIVATE_PYTHON) $^ > $@
+u_indices_gen_deps := \
+	$(MESA_TOP)/src/gallium/auxiliary/indices/u_indices_gen.py
 
-$(intermediates)/indices/u_indices_gen.c \
-$(intermediates)/indices/u_unfilled_gen.c \
-$(intermediates)/util/u_format_srgb.c: $(intermediates)/%.c: $(LOCAL_PATH)/%.py
-	$(transform-generated-source)
+$(intermediates)/indices/u_indices_gen.c: $(u_indices_gen_deps)
+	@mkdir -p $(dir $@)
+	$(hide) $(MESA_PYTHON3) $< > $@
+
+u_unfilled_gen_deps := \
+	$(MESA_TOP)/src/gallium/auxiliary/indices/u_unfilled_gen.py
+
+$(intermediates)/indices/u_unfilled_gen.c: $(u_unfilled_gen_deps)
+	@mkdir -p $(dir $@)
+	$(hide) $(MESA_PYTHON3) $< > $@
 
 LOCAL_GENERATED_SOURCES += $(MESA_GEN_NIR_H)