RISC-V: Add xfail test case for indexed load overlap with SRC EEW < DEST EEW

RISC-V: Add xfail test case for indexed load overlap with SRC EEW < DEST EEW

Update in v2:
* Add change log to pr112431-34.c.

Original log:

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.

4418d55bcd1 RISC-V: Support highpart overlap for indexed load with SRC EEW < DEST EEW

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

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/base/pr112431-34.c: Remove xfail for vluxei8 check.
	* gcc.target/riscv/rvv/base/pr112431-28.c: New test.
	* gcc.target/riscv/rvv/base/pr112431-29.c: New test.
	* gcc.target/riscv/rvv/base/pr112431-30.c: New test.
	* gcc.target/riscv/rvv/base/pr112431-31.c: New test.
	* gcc.target/riscv/rvv/base/pr112431-32.c: New test.
	* gcc.target/riscv/rvv/base/pr112431-33.c: New test.

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