MLK-9785-1 usb: host: ehci-hcd: enable park mode

MLK-9785-1 usb: host: ehci-hcd: enable park mode

Enable park mode will improve the performance a lot at USB ethernet use
case, but a little at USB mass storage use case, and it is not harm from
the tests. Below the performance comparison at imx6sl:

USB Ethernet (Mbps)
	Default			Enable Park
TX	192			262
RX	262			290

USB Mass Storage (MB/s)
Read	21.8			22.9
Write	19.5			22.8

This patch is used for freescale internal.

Signed-off-by: Peter Chen <peter.chen@freescale.com>
(cherry picked from commit b2289a78958859cff37508e4db0314463f33c2e0)