USB event poll support

This patch adds USB event poll support, which could be used in usbkbd
and other usb devices driver when the asynchronous interrupt
processing is supported.

Signed-off-by: Zhang Wei <wei.zhang@freescale.com>

README

@@ -901,6 +901,9 @@ The following options need to be configured:
 			CONFIG_USB_CONFIG
 				for differential drivers: 0x00001000
 				for single ended drivers: 0x00005000
+			CFG_USB_EVENT_POLL
+				May be defined to allow interrupt polling
+				instead of using asynchronous interrupts
 
 - USB Device:
 		Define the below if you wish to use the USB console.

common/usb_kbd.c

@@ -129,7 +129,11 @@ static int usb_kbd_testc(void)
 static int usb_kbd_getc(void)
 {
 	char c;
-	while(usb_in_pointer==usb_out_pointer);
+	while(usb_in_pointer==usb_out_pointer) {
+#ifdef CFG_USB_EVENT_POLL
+		usb_event_poll();
+#endif
+	}
 	if((usb_out_pointer+1)==USB_KBD_BUFFER_LEN)
 		usb_out_pointer=0;
 	else

include/usb.h

@@ -180,6 +180,7 @@ int submit_control_msg(struct usb_device *dev, unsigned long pipe, void *buffer,
 			int transfer_len,struct devrequest *setup);
 int submit_int_msg(struct usb_device *dev, unsigned long pipe, void *buffer,
 			int transfer_len, int interval);
+void usb_event_poll(void);
 
 /* Defines */
 #define USB_UHCI_VEND_ID 0x8086