usb: hub: fix power good delay timing

usb_hub_power_on() currently waits for the maximum of (a) the hub port's
power output to become good, (b) the max time the USB specification
allows a device to take to connect.

However, these two operations must occur in series rather than in
parallel. First, the power supply ramps up to the level required to
power the USB device, and then the device may take a certain amount of
time to connect (assert D+/D- pullups).

Related, the maximum time that a device has to assert pullups is 1s not
100ms.

This is explained in "Connect Timing ECN.pdf", itself part of
usb_20_042814.zip from www.usb.org.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
usb: hub: remove CONFIG_USB_HUB_MIN_POWER_ON_DELAY

Now that we wait the correct specification-mandated time at the end of
usb_hub_power_on(), I suspect that CONFIG_USB_HUB_MIN_POWER_ON_DELAY has
no purpose.

For cm_t35.h, we already wait longer than the original MIN_POWER_ON_DELAY,
so this change is safe.

For gw_ventana.h, we will wait as long as the original MIN_POWER_ON_DELAY
iff pgood_delay was at least 200ms. I'm not sure if this is the case or
not, hence I've CC'd relevant people to test this change.

Cc: Igor Grinberg <grinberg@compulab.co.il>
Cc: Tim Harvey <tharvey@gateworks.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>