drm/amdgpu/amdgpu_dm: fix kernel-doc markups

drm/amdgpu/amdgpu_dm: fix kernel-doc markups

There are 4 undocumented fields at struct amdgpu_display_manager.

Add documentation for them, fixing those warnings:

	drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h:544: warning: Function parameter or member 'dmub_outbox_params' not described in 'amdgpu_display_manager'
	drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h:544: warning: Function parameter or member 'num_of_edps' not described in 'amdgpu_display_manager'
	drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h:544: warning: Function parameter or member 'disable_hpd_irq' not described in 'amdgpu_display_manager'
	drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h:544: warning: Function parameter or member 'dmub_aux_transfer_done' not described in 'amdgpu_display_manager'
	drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h:544: warning: Function parameter or member 'delayed_hpd_wq' not described in 'amdgpu_display_manager'

Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>