platform: andes/ae350: Add fw_platform_init for platform initialization

This patch adds fw_platform_init() to initialize ae350 platform.name
and platform.hart_count by parsing device tree.

Signed-off-by: Yu Chien Peter Lin <peterlin@andestech.com>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>
Reviewed-by: Anup Patel <anup@brainfault.org>