DynamicTablesPkg: DGB2: Update DBG2_DEBUG_PORT_DDI

DynamicTablesPkg: DGB2: Update DBG2_DEBUG_PORT_DDI

This patch was originally merged in edk2 master at
6814256083a90ef218e7ae240e51922045175df1. However, this was
later reverted at db8382ef5e44bd07654fb4726b77f3c329210561
as it was merged during the Soft Feature Freeze for
edk2-stable201903.

Resubmitting this patch as the edk2 merge window is now open.

The DBG2_DEBUG_PORT_DDI() macro supports adding only one
Generic Base Address Register. Therefore, removed the
superfluous parameter NumReg and updated the macro to
use DBG2_NUMBER_OF_GENERIC_ADDRESS_REGISTERS which has
a value 1.

Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Alexei Fedorov <alexei.fedorov@arm.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>
Reviewed-by: Alexei Fedorov <alexei.fedorov@arm.com>