drm/i915: Explain the magic numbers for AUX SYNC/precharge length

drm/i915: Explain the magic numbers for AUX SYNC/precharge length

[ Upstream commit 26bfc3f36f2104c174dfc72415547d5c28ef3f1c ]

Replace the hardcoded final numbers in the AUX SYNC/precharge
setup, and derive those from numbers from the (e)DP specs.

The new functions can serve as the single point of truth for
the number of SYNC pulses we use.

Cc: Jouni Högander <jouni.hogander@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230329172434.18744-2-ville.syrjala@linux.intel.com
Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Stable-dep-of: 2d6f2f79e065 ("drm/i915: Use 18 fast wake AUX sync len")
Signed-off-by: Sasha Levin <sashal@kernel.org>