efi/capsule-loader: Explicitly include linux/io.h for page_to_phys()

Through a labyrinthian sequence of includes, usage of page_to_phys() 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/20191126165417.22423-7-sean.j.christopherson@intel.comSigned-off-by: Ingo Molnar <mingo@kernel.org>

drivers/firmware/efi/capsule-loader.c

@@ -11,6 +11,7 @@
 #include <linux/module.h>
 #include <linux/miscdevice.h>
 #include <linux/highmem.h>
+#include <linux/io.h>
 #include <linux/slab.h>
 #include <linux/mutex.h>
 #include <linux/efi.h>