linux-user: update comments to point to tcg_exec_init()

linux-user: update comments to point to tcg_exec_init()

cpu_init() was replaced by cpu_create() since 2.12 but comments
weren't updated. So update stale comments to point that page
sizes arei actually initialized by tcg_exec_init(). Also move
another qemu_host_page_size related comment before tcg_exec_init()
where it belongs.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <1526557877-293151-1-git-send-email-imammedo@redhat.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>