bus: ti-sysc: Drop legacy idle quirk handling

There are no more users that need the legacy idle quirk so let's drop
the legacy idle quirk handling. This simplifies the PM code to just
sysc_pm_ops with unified handling for all the interconnect targets.

Reviewed-by: Dhruva Gole <d-gole@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>