xen/arm: flush icache as well when XEN_DOMCTL_cacheflush is issued

xen/arm: flush icache as well when XEN_DOMCTL_cacheflush is issued

When the toolstack modifies memory of a running ARM VM it may happen
that the underlying memory of a current vCPU PC is changed. Without
flushing the icache the vCPU may continue executing stale instructions.

Also expose the xc_domain_cacheflush through xenctrl.h.

Signed-off-by: Tamas K Lengyel <tamas.lengyel@zentific.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>