make: pass IDF_ENV_FPGA=n to confgen and mconf

Fixes the following warnings:

warning: IDF_ENV_FPGA has 'option env="IDF_ENV_FPGA"', but the environment variable IDF_ENV_FPGA is not set

make/project_config.mk

@@ -92,6 +92,7 @@ define RunConfGen
 		--env "COMPONENT_KCONFIGS_PROJBUILD_SOURCE_FILE=$(COMPONENT_KCONFIGS_PROJBUILD_SOURCE_FILE)" \
 		--env "COMPONENT_SDKCONFIG_RENAMES=$(strip $(COMPONENT_SDKCONFIG_RENAMES))" \
 		--env "IDF_CMAKE=n" \
+		--env "IDF_ENV_FPGA=n" \
 		$(DEFAULTS_ARG) \
 		--output config ${SDKCONFIG} \
 		--output makefile $(SDKCONFIG_MAKEFILE) \
@@ -121,6 +122,7 @@ define RunMenuConf
 	COMPONENT_KCONFIGS_SOURCE_FILE="$(COMPONENT_KCONFIGS_SOURCE_FILE)" \
 	COMPONENT_KCONFIGS_PROJBUILD_SOURCE_FILE="$(COMPONENT_KCONFIGS_PROJBUILD_SOURCE_FILE)" \
 	IDF_CMAKE=n \
+	IDF_ENV_FPGA=n \
 	$(MENUCONFIG_CMD) $(IDF_PATH)/Kconfig
 endef