xen: arm: introduce concept of modules which can be in RAM at start of day

xen: arm: introduce concept of modules which can be in RAM at start of day

The intention is that these will eventually be filled in with
information from the bootloader, perhaps via a DTB binding.

Allow for 2 modules (kernel and initrd), plus a third pseudo-module
which is the hypervisor itself. Currently we neither parse nor do
anything with them.

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