RISC-V: Update testsuite due to -march string relaxation

RISC-V: Update testsuite due to -march string relaxation

We has relaxed -march string, it no longer require canonical order, so
we need update some of those testcase.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/arch-23.c: Update test.
	* gcc.target/riscv/arch-27.c: Ditto.
	* gcc.target/riscv/arch-28.c: Ditto.
	* gcc.target/riscv/attribute-10.c: Ditto.