xen/arm: bootfdt: Make process_chosen_node() return int

xen/arm: bootfdt: Make process_chosen_node() return int

At the boot time, it is saner to stop booting early if an error occurs
when parsing the device tree chosen node, rather than seeing random
behavior afterwards. Therefore, this commit changes the return type of
the process_chosen_node() from void to int, and return correct errno
based on the error type.

Signed-off-by: Henry Wang <Henry.Wang@arm.com>
Reviewed-by: Michal Orzel <michal.orzel@amd.com>
Acked-by: Julien Grall <jgrall@amazon.com>