virt: vbox: Explicitly include linux/io.h to pick up various defs

Through a labyrinthian sequence of includes, usage of page_to_phys(),
virt_to_phys() and out*() is dependent on the include of asm/io.h in
x86's asm/realmode.h, which is included in x86's asm/acpi.h and thus by
linux/acpi.h.  Explicitly include linux/io.h to break the dependency on
realmode.h so that a future patch can remove the realmode.h include from
acpi.h without breaking the build.
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Link: https://lkml.kernel.org/r/20191126165417.22423-8-sean.j.christopherson@intel.comSigned-off-by: Ingo Molnar <mingo@kernel.org>

drivers/virt/vboxguest/vboxguest_core.c

@@ -6,6 +6,7 @@
  */
 
 #include <linux/device.h>
+#include <linux/io.h>
 #include <linux/mm.h>
 #include <linux/sched.h>
 #include <linux/sizes.h>

drivers/virt/vboxguest/vboxguest_utils.c

@@ -7,6 +7,7 @@
  */
 
 #include <linux/errno.h>
+#include <linux/io.h>
 #include <linux/kernel.h>
 #include <linux/mm.h>
 #include <linux/module.h>