usb: host: xhci: Change L1 timeout default to 128us

L1 timeout default is set to 512us which reduces the
possibility of entering in to L1 state for smaller
service interval value. This impacts the power saving
due to L1. Hence set the timeout to lowest allowed value
i.e. 128us.

Change-Id: Ic261ba25ddd8097f43dffa5f6af88d97f0e417d3
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>