drm/bridge: anx7625: Use common macros for DP power sequencing commands

The DRM DP code has macros for the DP power sequencing commands. Use
them in the anx7625 driver instead of raw numbers.

Fixes: 548b512e ("drm/bridge: anx7625: send DPCD command to downstream")
Fixes: 27f26359 ("drm/bridge: anx7625: Set downstream sink into normal status")
Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
Reviewed-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Signed-off-by: Robert Foss <rfoss@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230710090929.1873646-1-wenst@chromium.org