Add macros for NVIDIA 16550 UART specific debug port subtype in both DBG2 as well as SPCR header file. Signed-off-by: Ashish Singhal <ashishsingha@nvidia.com> Reviewed-by: Samer El-Haj-Mahmoud <Samer.El-Haj-Mahmoud@arm.com> Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn> Reviewed-by: Sunny Wang <sunny.wang@arm.com>