RISC-V: Add ABI requirement for XTheadFMemIdx tests

RISC-V: Add ABI requirement for XTheadFMemIdx tests

The XTheadFMemIdx tests set the required ABI for RV32, but not
for RV64, which has the effect that the tests are expected to
succeed for RV64/LP64.  Let's set the ABI to LP64D in these
tests to clarify the requirements.

Signed-off-by: Christoph Müllner <christoph.muellner@vrull.eu>
gcc/testsuite/ChangeLog:

	* gcc.target/riscv/xtheadfmemidx-index-update.c: Add ABI.
	* gcc.target/riscv/xtheadfmemidx-index-xtheadbb-update.c: Likewise.
	* gcc.target/riscv/xtheadfmemidx-index-xtheadbb.c: Likewise.
	* gcc.target/riscv/xtheadfmemidx-index.c: Likewise.
	* gcc.target/riscv/xtheadfmemidx-uindex-update.c: Likewise.
	* gcc.target/riscv/xtheadfmemidx-uindex-xtheadbb-update.c: Likewise.
	* gcc.target/riscv/xtheadfmemidx-uindex-xtheadbb.c: Likewise.
	* gcc.target/riscv/xtheadfmemidx-uindex.c: Likewise.