tests/acpi: Add empty ACPI SRAT data file for RISC-V

tests/acpi: Add empty ACPI SRAT data file for RISC-V

As per process documented (steps 1-3) in bios-tables-test.c, add
empty AML data file for RISC-V ACPI SRAT table and add the entry
in bios-tables-test-allowed-diff.h.

Signed-off-by: Haibo Xu <haibo1.xu@intel.com>
Reviewed-by: Sunil V L <sunilvl@ventanamicro.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <0e30216273f2f59916bc651350578d8e8bc3a75f.1723172696.git.haibo1.xu@intel.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>