irqchip: omap-intc: enable TURBO idle mode

When TURBO bit is set in the INTC_IDLE register,
the input synchronizer clock will be autogated
based on activity on the INTC.

Because this idle mode increases the interrupt
latency by 2 clock cycles, we're only enabling
it during suspend.

Acked-by: Jason Cooper <jason@lakedaemon.net>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>