hvmloader: clear the xenbus event-channel when we're done with it.

Otherwise a later xenbus client that naively waits for the rising edge
could get stuck.

Signed-off-by: Tim Deegan <Tim.Deegan@citrix.com>

tools/firmware/hvmloader/util.h

@@ -69,6 +69,9 @@ void pci_write(uint32_t devfn, uint32_t reg, uint32_t len, uint32_t val);
 #define pci_writew(devfn, reg, val) (pci_write(devfn, reg, 2, (uint16_t)val))
 #define pci_writel(devfn, reg, val) (pci_write(devfn, reg, 4, (uint32_t)val))
 
+/* Get a pointer to the shared-info page */
+struct shared_info *get_shared_info(void);
+
 /* Get CPU speed in MHz. */
 uint16_t get_cpu_mhz(void);