drm/i915/xe3lpd: Update HDCP rekeying bit

The TRANS_DDI_FUNC_CTL bit used to enable/disable HDCP rekeying
has moved from bit 12 (Xe2) to bit 15 (Xe3); update the RMW
toggle accordingly.
Also drop the misleading workaround comment tag on this function
since disabling of HDCP rekeying is something that happens on
all platforms, not just those impacted by that workaround.
While we're here, also re-order the if/else ladder to use
standard "newest platform first" order.

v2: add additional definition instead of function, commit message typo
fix and update.
v3: restore lost conditional from v2.
v4: subject line and subject message updated, fix the if ladder order,
fix the bit definition order.
v5: Add the bspec link and remove the Wa comment tag
v6: Rebase over new changes
v7: Fix commit subject and message, reladder the if/else blocks

Bspec: 69964
Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241104185055.739605-1-suraj.kandpal@intel.com