drm/bridge: it6505: fix HDCP Bstatus check

When HDCP is activated,
a DisplayPort source receiving CP_IRQ from the sink
shall check Bstatus from DPCD and process the corresponding value

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Hermes Wu <hermes.wu@ite.com.tw>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20241230-v7-upstream-v7-5-e0fdd4844703@ite.corp-partner.google.com