bus: ti-sysc: Handle missed no-idle property in addition to no-idle-on-init

We have ti,no-idle in use in addition to ti,no-idle-on-init but we're
missing handling for it in the ti-sysc interconnect target module driver.

Let's also group the idle defines together and update the binding
documentation for it.

Cc: devicetree@vger.kernel.org
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>