usb: host: ehci: adding regulator framework in ehci-omap.c driver.

OMAP3 has three HS USB ports so it can have three different regulator
for each PHY connected to each port.

Currently these regulators are assumed to be optional and driver doesn't
fail but continue with the initialization if it doesn't get any regulators.

Regulator supply names has to be mapped in board files as 'hsusbN' where
'N' is port number and can be {0, 1 ,2}.

Signed-off-by: Ajay Kumar Gupta <ajay.gupta@ti.com>
Signed-off-by: Felipe Balbi <felipe.balbi@nokia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>