xen/arm: don't add duplicate boot modules, introduce domU flag

xen/arm: don't add duplicate boot modules, introduce domU flag

Don't add duplicate boot modules (same kind and same start address),
they are freed later, we don't want to introduce double-free errors.

Introduce a domU flag in struct bootmodule and struct bootcmdline. Set
it for kernels and ramdisks of "xen,domain" nodes to avoid getting
confused in kernel_probe, where we try to guess which is the dom0 kernel
and initrd to be compatible with all versions of the multiboot spec.

boot_module_find_by_kind and boot_cmdline_find_by_kind automatically
check for !domU entries (they are only used for non-domU modules).

Signed-off-by: Stefano Stabellini <stefanos@xilinx.com>
Reviewed-by: Julien Grall <julien.grall@arm.com>