drivers: gpu: Move prototype declarations to header file radeon_mode.h from radeon_atombios.c and radeon_combios.c

Move prototype declarations of functions radeon_get_encoder_enum() and
radeon_link_encoder_connector() to header file drm/radeon/radeon_mode.h
because they are used by more than one file.

This eliminates the following warnings in drm/radeon/radeon_encoders.c:
drivers/gpu/drm/radeon/radeon_encoders.c:86:1: warning: no previous prototype for ‘radeon_get_encoder_enum’ [-Wmissing-prototypes]
drivers/gpu/drm/radeon/radeon_encoders.c:162:1: warning: no previous prototype for ‘radeon_link_encoder_connector’ [-Wmissing-prototypes]

Signed-off-by: Rashika Kheria <[e-mail]>
Reviewed-by: Josh Triplett <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/radeon/radeon_atombios.c

···
 #include "atom.h"
 #include "atom-bits.h"
 
-/* from radeon_encoder.c */
-extern uint32_t
-radeon_get_encoder_enum(struct drm_device *dev, uint32_t supported_device,
-			uint8_t dac);
-extern void radeon_link_encoder_connector(struct drm_device *dev);
 extern void
 radeon_add_atom_encoder(struct drm_device *dev, uint32_t encoder_enum,
 			uint32_t supported_device, u16 caps);

drivers/gpu/drm/radeon/radeon_combios.c

···
 #include <asm/pci-bridge.h>
 #endif /* CONFIG_PPC_PMAC */
 
-/* from radeon_encoder.c */
-extern uint32_t
-radeon_get_encoder_enum(struct drm_device *dev, uint32_t supported_device,
-			uint8_t dac);
-extern void radeon_link_encoder_connector(struct drm_device *dev);
-
 /* from radeon_legacy_encoder.c */
 extern void
 radeon_add_legacy_encoder(struct drm_device *dev, uint32_t encoder_enum,

drivers/gpu/drm/radeon/radeon_mode.h

···
 			    struct radeon_i2c_bus_rec *i2c_bus,
 			    uint16_t connector_object_id,
 			    struct radeon_hpd *hpd);
+extern uint32_t
+radeon_get_encoder_enum(struct drm_device *dev, uint32_t supported_device,
+			uint8_t dac);
+extern void radeon_link_encoder_connector(struct drm_device *dev);
 
 extern enum radeon_tv_std
 radeon_combios_get_tv_info(struct radeon_device *rdev);