xen/arm: flush dcache after memcpy'ing the kernel image

xen/arm: flush dcache after memcpy'ing the kernel image

After memcpy'ing the kernel in guest memory we need to flush the dcache
to make sure that the data actually reaches the memory before we start
executing guest code with caches disabled.

copy_from_paddr is the function that does the copy, so add a
flush_xen_dcache_va_range there.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Committed-by: Ian Campbell <ian.campbell@citrix.com>