drm/amd/display: fix kernel-doc issues in dc.h

Fix these kernel-doc complaints:

drivers/gpu/drm/amd/display/dc/dc.h:505: warning: cannot understand function prototype: 'struct dc_clocks '
dc.h:472: warning: Enum value 'MPC_SPLIT_AVOID' not described in enum 'pipe_split_policy'
dc.h:472: warning: Enum value 'MPC_SPLIT_AVOID_MULT_DISP' not described in enum 'pipe_split_policy'
dc.h:532: warning: Incorrect use of kernel-doc format:          * @fw_based_mclk_switching

Fixes: ea76895f ("drm/amd/display: Document pipe split policy")
Fixes: 1682bd1a ("drm/amd/display: Expand kernel doc for DC")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Leo Li <sunpeng.li@amd.com>
Cc: amd-gfx@lists.freedesktop.org
Cc: David Airlie <airlied@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>