USB: OTG: prevent idle standalone PC when USB cable is connected.

When USB cable is connected, the mass storage function in the
device will get interrupts for every 3ms. Entering and exiting the
idle standalone PC itself will take around 3ms on 8960. Hence allowing
idle standalone PC when USB cable is connected causes processor to
spend most of the time in entering and exiting the idle standalone PC.
Hence Vote for minimum DMA latency to prevent idle standalone PC
when USB cable is connected.

Change-Id: Id625dc01f253ed553b2f65f08900022a8c6e1daa
Signed-off-by: Anji jonnala <anjir@codeaurora.org>