Platform/ARM/N1SDP: Add initial N1SDP platform support

Neoverse N1 System Development Platform (N1SDP) is an infrastructure
segment development platform. It includes a Neoverse N1 SoC and an
IOFPGA that provides access to low-bandwidth peripherals. It
also enables development of CCIX-enabled FPGA accelerators.

Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Cc: Leif Lindholm <leif@nuviainc.com>
Signed-off-by: Pranav Madhu <pranav.madhu@arm.com>
Reviewed-by: Leif Lindholm <leif@nuviainc.com>
Reviewed-by: Thomas Abraham <thomas.abraham@arm.com>