ACPI: support BGRT table on RISC-V

ACPI: support BGRT table on RISC-V

The BGRT table is used to display a vendor logo in the boot process.
There is no good reason why RISC-V should not support it.

Remove the architecture constraint.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Acked-by: Rafael J. Wysocki <rafael@kernel.org>
Reviewed-by: Sunil V L <sunilvl@ventanamicro.com>
Link: https://lore.kernel.org/r/20250729131535.522205-3-heinrich.schuchardt@canonical.com
Signed-off-by: Paul Walmsley <pjw@kernel.org>