drivers: gpu: Move prototype declaration to header file radeon_mode.h from atombios_i2c.c

Move prototype declaration of function radeon_atom_copy_swap() to header
file drm/radeon/radeon_mode.h because it is used by more than one file.

This eliminates the following warnings in drm/radeon/atombios_dp.c:
drivers/gpu/drm/radeon/atombios_dp.c:53:6: warning: no previous prototype for ‘radeon_atom_copy_swap’ [-Wmissing-prototypes]
Signed-off-by: Rashika Kheria <rashika.kheria@gmail.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/atombios_i2c.c

@@ -27,8 +27,6 @@
 #include "radeon.h"
 #include "atom.h"
 
-extern void radeon_atom_copy_swap(u8 *dst, u8 *src, u8 num_bytes, bool to_le);
-
 #define TARGET_HW_I2C_CLOCK 50
 
 /* these are a limitation of ProcessI2cChannelTransaction not the hw */

drivers/gpu/drm/radeon/radeon_mode.h

@@ -666,6 +666,7 @@ extern void radeon_atom_ext_encoder_setup_ddc(struct drm_encoder *encoder);
 extern struct drm_encoder *radeon_get_external_encoder(struct drm_encoder *encoder);
 extern int radeon_dp_i2c_aux_ch(struct i2c_adapter *adapter, int mode,
 				u8 write_byte, u8 *read_byte);
+void radeon_atom_copy_swap(u8 *dst, u8 *src, u8 num_bytes, bool to_le);
 
 extern void radeon_i2c_init(struct radeon_device *rdev);
 extern void radeon_i2c_fini(struct radeon_device *rdev);