[ARM] Don't use of /templates for guest templates

This patch removes the use of /templates device tree path for
keeping guest templates. Instead we now load guest device tree
directly from FDT file on file system.

If someone wants to disable filesystem then he/she will have to
use the old method of keeping reference guest device tree under
/templates device tree path.

Signed-off-by: Anup Patel <anup@brainfault.org>