Change USB port scanning procedure and timeout handling in the
following ways:

1)
The power-on delay in usb_hub_power_on() is now reduced to a value of
max(100ms, "hub->desc.bPwrOn2PwrGood * 2"). The code does not wait
using mdelay, instead usb_hub_power_on() will wait before querying
the device in the scanning loop later. The total connection timeout for
this hub, which is (1 second + hub->desc.bPwrOn2PwrGood * 2) is
calculated and will be used in the following per-port scanning loop as
the timeout to detect active USB devices on this hub.

2)
Don't delay the minimum delay (for power to stabilize) in
usb_hub_power_on(). Instead skip querying these devices in the scanning
loop usb_scan_port() until the delay time is reached.

3)
The ports are now scanned in a quasi parallel way. The current code did
wait for each (unconnected) port to reach its timeout and only then
continue with the next port. This patch now changes this to scan all
ports of all USB hubs quasi simultaneously. For this, all ports are added
to a scanning list in usb_hub_configure_ports(). The list is later scanned
in usb_device_list_scan() until all ports are ready by either a) reaching
the connection timeout (calculated earlier), or by b) detecting a USB
device. This results in a faster USB scan time as the recursive scanning
of USB hubs connected to the hub that's currently being scanned will
start earlier.

4)
Ports with overcurrent detection will get scanned multiple times if OC
condition is detected (PORT_OVERCURRENT_MAX_SCAN_COUNT).

Without patch:

    $ time usb
    usb: USB: scanning bus for devices...
    usb: 17 USB Device(s) found
    time: 10344ms

With patch:

    $ time usb
    usb: USB: scanning bus for devices...
    usb: 17 USB Device(s) found
    time: 4529ms

Delta: ~6 seconds

Signed-off-by: Primoz Fiser <primoz.fiser@norik.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>