ACPICA: Add structure definitions for RISC-V RHCT

ACPICA commit 82afd0434e79f74b96a6be88115ddc8343a1ba40

RISC-V Hart Capabilities Table (RHCT) is a new static table.
The ECR to add RHCT is approved by the UEFI forum and will be
available in the next version of the ACPI spec.

Link: https://github.com/acpica/acpica/commit/82afd043


Signed-off-by: Sunil V L <sunilvl@ventanamicro.com>
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>