xen/arm: traps: Update the correct PC when inject a virtual SError to the guest

xen/arm: traps: Update the correct PC when inject a virtual SError to the guest

When injecting a virtual Abort to the guest, we want to update the guest
PC so it can re-execute the HVC/SMC once it has handled the SError.

This is unfortunately not the case when the SError is synchronized on
entry from the guest. As the SError will be received while running in
hypervisor context, we will update the PC of hypervisor context (i.e
the trap).

Rework inject_vabt_exception so it uses the guest context rather than
the current one.

Signed-off-by: Julien Grall <julien.grall@arm.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>
Release-acked-by: Juergen Gross <jgross@suse.com>