libpayload: Correct port power settings for EHCI root hub

Enable power on EHCI root hub ports only if the controller supports it.
Wait 20ms for the power to become stable.

Change-Id: I8897756ed2bfcb88408fe5e9f9e3f8af5dd900ac
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: http://review.coreboot.org/1078
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>

payloads/libpayload/drivers/usb/ehci_private.h

@@ -49,6 +49,7 @@ typedef volatile u32 portsc_t;
 
 typedef volatile struct {
 #define HCS_NPORTS_MASK 0xf
+#define HCS_PORT_POWER_CONTROL 0x10
 	u8 caplength;
 	u8 res1;
 	u16 hciversion;