inmates: x86: align code after last level of page tables

The header contains the page tables but the last level (pd) contained the
code right after the first entry. Calls to map_range would actually
overwrite the inmates code.
This patch makes sure the code will start on the next page.

Signed-off-by: Henning Schild <henning.schild@siemens.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>