boards: arm64: Add Intel SoC FPGA Agilex5 development kit board

This is the initial Zephyr support for Intel SoC FPGA Agilex5 support.
Agilex5 has dual-core 64-bit ARM Cortex*-A55 and dual-core 64bit
ARM Cortex*-A76.

The Zephyr will need to be loaded by Intel Arm Trusted Firmware (ATF).
Agilex5 Zephyr boot flow:
  FSBL:ATF BL2(EL3) -> ATF BL31(EL3) -> OS:Zephyr(EL1)

Intel ATF can be loaded from:
  https://github.com/altera-opensource/arm-trusted-firmware.git



Signed-off-by: Teik Heng Chong <teik.heng.chong@intel.com>
Signed-off-by: Girisha Dengi <girisha.dengi@intel.com>