ACPICA: Headers: Add RISC-V SBI Subtype to DBG2

ACPICA commit 6f4c900bcf9ca065129353f17a83773aa58095aa

Include the RISC-V SBI debugging subtype as documented in DBG2
dated April 10, 2023 [1].

Link: https://learn.microsoft.com/en-us/windows-hardware/drivers/bringup/acpi-debug-port-table # [1]
Link: https://github.com/acpica/acpica/commit/6f4c900b


Signed-off-by: Sia Jee Heng <jeeheng.sia@starfivetech.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>