xen/altp2m: set access_required properly for all altp2ms

xen/altp2m: set access_required properly for all altp2ms

For the hostp2m, access_required starts off as 0, then it can be
set with xc_domain_set_access_required(). However, all the altp2ms
set it to 1 on init, and ignore both the hostp2m and the hypercall.
This patch sets access_required to the value from the hostp2m
on altp2m init, and propagates the values received via hypercall
to all the active altp2ms, when applicable.

Signed-off-by: Razvan Cojocaru <rcojocaru@bitdefender.com>
Acked-by: Tamas K Lengyel <tamas@tklengyel.com>
Reviewed-by: George Dunlap <george.dunlap@citrix.com>
Acked-by: Julien Grall <julien.grall@arm.com>