bus: ti-sysc: rework the reset handling

If reset controllers are assigned to the ti-sysc target-module, only
ti-sysc is going to be able to control these. Thus, remove all the
disable_on_idle flag usage, and assert/de-assert the reset always
in the idle path. Otherwise the reset signal will always just be
de-asserted.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>