ARM: shmobile: Lager USB0 cable detection workaround

Add Lager board code to check the PWEN GPIO signal and refuse to
allow probe of the USBHS driver in case of DIP misconfiguration.

For correct operation Lager DIP switches SW5 and SW6 shall be
configured in 2-3 position to enable USB Function support.

If the DIP switch is configured incorrectly then the user can
simply adjust the hardware and either reboot or use the bind interface
to try to probe again:

# echo renesas_usbhs > /sys/bus/platform/drivers/renesas_usbhs/bind

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>