bus: ti-sysc: Allow QUIRK_LEGACY_IDLE even if legacy_mode is not set

We need to specify QUIRK_LEGACY_IDLE for device drivers that still have
pm_runtime_irq_safe() set like 8250.

Tested-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>