cnss2: Use external configurations

Add option to select configurations from other places
such as yocto recipe.

Change-Id: I9ce971f3548d65630642f0b467515090f10f1480

Makefile

@@ -9,6 +9,7 @@ WLAN_PLATFORM_ROOT = $(shell pwd)
 # so enable all flags (including debug flag CONFIG_CNSS2_DEBUG) by
 # default.
 KBUILD_OPTIONS := WLAN_PLATFORM_ROOT=$(WLAN_PLATFORM_ROOT)
+ifeq ($(USE_EXTERNAL_CONFIGS),)
 KBUILD_OPTIONS += CONFIG_CNSS_OUT_OF_TREE=y
 KBUILD_OPTIONS += CONFIG_CNSS2=m
 KBUILD_OPTIONS += CONFIG_ICNSS2=m
@@ -22,6 +23,7 @@ KBUILD_OPTIONS += CONFIG_CNSS_GENL=m
 KBUILD_OPTIONS += CONFIG_WCNSS_MEM_PRE_ALLOC=m
 KBUILD_OPTIONS += CONFIG_CNSS_UTILS=m
 endif
+endif
 
 all:
 	$(MAKE) -C $(KERNEL_SRC) M=$(M) modules $(KBUILD_OPTIONS)