xen/arm: vgic: Drop iactive, ipend, pendsgi field

xen/arm: vgic: Drop iactive, ipend, pendsgi field

The current VGIC code doesn't support to change the pending and active status
of an IRQ via the (re-)distributor.

Futhermore, all the access size wasn't support correctly and some
registers was implemented as write-ignore. The latter make very
difficult for a kernel developer to find that we don't support R/W to
those registers.

Make the support consistent:
    - read will return 0 (RAZ)
    - write will print an error and inject a data abort to the guest

Also, those fields was never set and field such as ipend and pendsgi was
doing the same jobs.

Rather than wasting memory, we should better drop it. We could re-introduce
them if we need it when the support will be made.

Signed-off-by: Julien Grall <julien.grall@linaro.org>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
[ ijc -- s/XENLOG_ERR/XENLOG_G_ERR/g ]