xen/efi: Directly include needed headers

I discovered that some needed stuff is defined/declared in headers
which are not included directly. Currently it works but if somebody
remove required headers from currently included headers then build
will break. So, just in case directly include all needed headers.

Signed-off-by: Daniel Kiper <daniel.kiper@oracle.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>