USB: musb: only turn off vbus in OTG hosts

Except on DaVinci, VBUS is now switched off as part of idling the
USB link (after a_wait_bcon) whenever a device is disconnected
from host.  This is correct for OTG hosts, where either SRP or
an ID interrupt could turn VBUS on again.

However, for non-OTG hosts there's no way to turn VBUS on again,
so the host becomes unusable.  And the procfs entry which once
allowed a manual workaround for this is now gone.

This patch adds an is_otg_enabled() check before scheduling the
switch-off timer in disconnect path, supporting a "classic host"
mode where SRP is unavailable.

[ dbrownell@users.sourceforge.net: tweak patch description ]
Signed-off-by: Ajay Kumar Gupta <ajay.gupta@ti.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/musb/musb_core.c

@@ -769,7 +769,7 @@ static irqreturn_t musb_stage2_irq(struct musb *musb, u8 int_usb,
 		case OTG_STATE_A_SUSPEND:
 			usb_hcd_resume_root_hub(musb_to_hcd(musb));
 			musb_root_disconnect(musb);
-			if (musb->a_wait_bcon != 0)
+			if (musb->a_wait_bcon != 0 && is_otg_enabled(musb))
 				musb_platform_try_idle(musb, jiffies
 					+ msecs_to_jiffies(musb->a_wait_bcon));
 			break;