RISC-V: Add xfail test case for highpart register overlap of vx/vf widen

RISC-V: Add xfail test case for highpart register overlap of vx/vf widen

We reverted below patch for register group overlap, add the related
insn test and mark it as xfail.  And we will remove the xfail
after we support the register overlap in GCC-15.

a23415d7572 RISC-V: Support highpart register overlap for widen vx/vf instructions

The below test suites are passed.
* The rv64gcv fully regression test.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/base/pr112431-22.c: New test.
	* gcc.target/riscv/rvv/base/pr112431-23.c: New test.
	* gcc.target/riscv/rvv/base/pr112431-24.c: New test.
	* gcc.target/riscv/rvv/base/pr112431-25.c: New test.
	* gcc.target/riscv/rvv/base/pr112431-26.c: New test.
	* gcc.target/riscv/rvv/base/pr112431-27.c: New test.

Signed-off-by: Pan Li <pan2.li@intel.com>