staging: vc04_services: fix up rpi firmware functions

The raspberrypi-firmware.h file should provide empty functions if we
aren't building in that option. This makes it easier to test-build
code, and not have odd warnings about unused variables if you just try
to #define away the functions.

Cc: Daniel Stone <[e-mail]>
Cc: "Noralf Trønnes" <[e-mail]>
Cc: Pranith Kumar <[e-mail]>
Cc: popcornmix <[e-mail]>
Cc: Eric Anholt <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

include/soc/bcm2835/raspberrypi-firmware.h

···
 	RPI_FIRMWARE_GET_DMA_CHANNELS =                       0x00060001,
 };
 
+#if IS_ENABLED(CONFIG_RASPBERRYPI_FIRMWARE)
 int rpi_firmware_property(struct rpi_firmware *fw,
 			  u32 tag, void *data, size_t len);
 int rpi_firmware_property_list(struct rpi_firmware *fw,
 			       void *data, size_t tag_size);
 struct rpi_firmware *rpi_firmware_get(struct device_node *firmware_node);
+#else
+static inline int rpi_firmware_property(struct rpi_firmware *fw, u32 tag,
+					void *data, size_t len)
+{
+	return 0;
+}
+
+static inline int rpi_firmware_property_list(struct rpi_firmware *fw,
+					     void *data, size_t tag_size)
+{
+	return 0;
+}
+
+static inline struct rpi_firmware *rpi_firmware_get(struct device_node *firmware_node)
+{
+	return NULL;
+}
+#endif
 
 #endif /* __SOC_RASPBERRY_FIRMWARE_H__ */