[hi3716c] Add custom prop file

build/core/Makefile
Add:
(1)
# -----------------------------------------------------------------
# gemtek.prop
INSTALLED_GTK_PROP_TARGET := $(TARGET_ROOT_OUT)/gemtek_default.prop
ALL_DEFAULT_INSTALLED_MODULES += $(INSTALLED_GTK_PROP_TARGET)

$(INSTALLED_GTK_PROP_TARGET):
        @echo Target buildinfo: $@
        @mkdir -p $(dir $@)
        $(hide) echo "#Gemtek-defined properties" > $@;
        build/tools/post_process_props.py $@
(2)
cat $(INSTALLED_GTK_PROP_TARGET) > $(TARGET_RECOVERY_ROOT_OUT)/gemtek_default.prop

build/CleanSpec.mk
Add:
 $(call add-clean-step, rm -rf $(PRODUCT_OUT)/root/gemtek_default.prop)

build/tools/post_process_props.py
Add:
(1)
 Put the modifications that you need to make into the /data/gemtek.prop into this
# function. The prop object has get(name) and put(name,value) methods.
def mangle_gtk_prop(prop):
    prop.put("hotkey0", "com.android.settings")
    prop.put("hotkey1", "com.android.settings")
    prop.put("hotkey2", "com.android.settings")
    prop.put("hotkey3", "com.android.settings")
    prop.put("hotkey4", "com.android.settings")
    prop.put("hotkey5", "com.android.settings")
    prop.put("hotkey6", "com.android.settings")
    prop.put("hotkey7", "com.android.settings")
(2)
elif filename.endswith("/gemtek_default.prop"):
    mangle_gtk_prop(properties)

Then check it in init.rc and copy the gemtek_default.prop to /data if gemtek.prop doesn't exist.
gemtek.prop is the copy that user could modify on.