Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/radeon/evergreen.c:1281:6: warning: no previous prototype for ‘evergreen_fix_pci_max_read_req_size’ [-Wmissing-prototypes]
 1281 | void evergreen_fix_pci_max_read_req_size(struct radeon_device *rdev)
 | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 drivers/gpu/drm/radeon/evergreen.c:2664:6: warning: no previous prototype for ‘evergreen_mc_stop’ [-Wmissing-prototypes]
 2664 | void evergreen_mc_stop(struct radeon_device *rdev, struct evergreen_mc_save *save)
 | ^~~~~~~~~~~~~~~~~
 drivers/gpu/drm/radeon/evergreen.c:2762:6: warning: no previous prototype for ‘evergreen_mc_resume’ [-Wmissing-prototypes]
 2762 | void evergreen_mc_resume(struct radeon_device *rdev, struct evergreen_mc_save *save)
 | ^~~~~~~~~~~~~~~~~~~
 drivers/gpu/drm/radeon/evergreen.c:2850:6: warning: no previous prototype for ‘evergreen_mc_program’ [-Wmissing-prototypes]
 2850 | void evergreen_mc_program(struct radeon_device *rdev)
 | ^~~~~~~~~~~~~~~~~~~~
 drivers/gpu/drm/radeon/evergreen.c:3710:5: warning: no previous prototype for ‘evergreen_mc_init’ [-Wmissing-prototypes]
 3710 | int evergreen_mc_init(struct radeon_device *rdev)
 | ^~~~~~~~~~~~~~~~~
 drivers/gpu/drm/radeon/evergreen.c:3769:6: warning: no previous prototype for ‘evergreen_print_gpu_status_regs’ [-Wmissing-prototypes]
 3769 | void evergreen_print_gpu_status_regs(struct radeon_device *rdev)
 | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 drivers/gpu/drm/radeon/evergreen.c:3797:6: warning: no previous prototype for ‘evergreen_is_display_hung’ [-Wmissing-prototypes]
 3797 | bool evergreen_is_display_hung(struct radeon_device *rdev)
 | ^~~~~~~~~~~~~~~~~~~~~~~~~
 drivers/gpu/drm/radeon/evergreen.c:4009:6: warning: no previous prototype for ‘evergreen_gpu_pci_config_reset’ [-Wmissing-prototypes]
 4009 | void evergreen_gpu_pci_config_reset(struct radeon_device *rdev)
 | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 drivers/gpu/drm/radeon/evergreen.c:4110:6: warning: no previous prototype for ‘sumo_rlc_fini’ [-Wmissing-prototypes]
 4110 | void sumo_rlc_fini(struct radeon_device *rdev)
 | ^~~~~~~~~~~~~
 drivers/gpu/drm/radeon/evergreen.c:4153:5: warning: no previous prototype for ‘sumo_rlc_init’ [-Wmissing-prototypes]
 4153 | int sumo_rlc_init(struct radeon_device *rdev)
 | ^~~~~~~~~~~~~
 drivers/gpu/drm/radeon/evergreen.c:4381:5: warning: no previous prototype for ‘evergreen_rlc_resume’ [-Wmissing-prototypes]
 4381 | int evergreen_rlc_resume(struct radeon_device *rdev)
 | ^~~~~~~~~~~~~
 drivers/gpu/drm/radeon/evergreen.c:4670:6: warning: no previous prototype for ‘evergreen_irq_suspend’ [-Wmissing-prototypes]
 4670 | void evergreen_irq_suspend(struct radeon_device *rdev)
 | ^~~~~~~~~~~~~~~~~~~~~

NB: Lots more of these - snipped for brevity

Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>