vpci: include xen/vmap.h to fix build on ARM

Patch b4f2116060 ("vpci/msix: fix PBA accesses") introduced call to
iounmap(), but not added corresponding include.

Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@epam.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Release-acked-by: Henry Wang <Henry.Wang@arm.com>

xen/drivers/vpci/vpci.c

@@ -19,6 +19,7 @@
 
 #include <xen/sched.h>
 #include <xen/vpci.h>
+#include <xen/vmap.h>
 
 /* Internal struct to store the emulated PCI registers. */
 struct vpci_register {