arm: socfpga: agilex: Probe DT for firewall setup

arm: socfpga: agilex: Probe DT for firewall setup

Update Agilex SPL code to implement device tree model
for firewall registers setup by using DTreg driver to
probe from device tree for the firewall settings instead
of calling firewall driver function.

Signed-off-by: Alif Zakuan Yuslaimi <alif.zakuan.yuslaimi@altera.com>
Reviewed-by: Tien Fong Chee <tien.fong.chee@altera.com>