drm/i915/tc: Block/unblock TC-cold in the PHY connect/disconnect hooks

Move blocking/unblocking the TC-cold power state to the platform
specific PHY connect / disconnect hooks. This allows for adjusting the
connect/disconnect sequence as required for each platform.

Reviewed-by: Mika Kahola <mika.kahola@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230323142035.1432621-17-imre.deak@intel.com