arch: arm: dts: agilex: Switch to using upstream Linux DT config

arch: arm: dts: agilex: Switch to using upstream Linux DT config

Migrate the legacy Agilex platform to use the upstream Linux device tree
configuration. This helps reduce maintenance overhead and aligns U-Boot
with the Linux kernel's DTS hierarchy and naming conventions.

This change improves consistency between U-Boot and Linux by removing
custom/legacy DTS handling and instead relying on the standardized
definitions provided by the upstream Linux DTS.

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