drm/i915: Fix DP_AUX_CH_CTL_TIME_OUT naming

Rename DP_AUX_CH_CTL_TIME_OUT_1600us to DP_AUX_CH_CTL_TIME_OUT_MAX, as
the meaning of the (3 << 26) value varies per platform, but it's always the
maximum timeout for that platform. Pre-CNL it means 1600us, and for CNL
it means 3200us.

v2:
-Split in to two patches (Rodrigo)

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: James Ausmus <james.ausmus@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171012213037.4245-1-james.ausmus@intel.com