[Feature request]For some ehci controller, qemu should implement using portsc[26-27]  to detect the speed of device.

for some ehci controller ,for example ehci controller on fsl_imx6,it using portsc[26-27] to decide a full speed device or high speed device was connected, hub-ehci.c should set the portsc[26-27] to return the right speed.

line:1001 in hub-ehci.c
        if (dev && dev->attached && (dev->speedmask & USB_SPEED_MASK_HIGH)) {
            val |= PORTSC_PED;
        }

below is the spec for fsl_imx6 USB PART.
PORTSC:27–26 :PSPD
Port Speed - Read Only.
This register field indicates the speed at which the port is operating.
00 Full Speed
01 Low Speed
10 High Speed
11 Undefined