xen/arm: vgic-v3: fix GICD_ISACTIVER range

xen/arm: vgic-v3: fix GICD_ISACTIVER range

The end should be GICD_ISACTIVERN not GICD_ISACTIVER.

See https://marc.info/?l=xen-devel&m=158527653730795 for a discussion on
what it would take to implement GICD_ISACTIVER/GICD_ICACTIVER properly.

We chose v1 instead of v2 of this patch to avoid spamming the console:
v2 adds a printk for every read, and reads can happen often.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
[Stefano: improve commit message]
Signed-off-by: Stefano Stabellini <stefano.stabellini@xilinx.com>
Acked-by: Julien Grall <jgrall@amazon.com>