RISC-V: Rename test[NFC]

Since I want to commit multiple tests which are fixing vsetvl bugs,
rename it to make testcases more easier maintain.

Committed as it is obvious.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/vsetvl/avl_use_bug-1.c: Moved to...
	* gcc.target/riscv/rvv/vsetvl/vsetvl_bug-1.c: ...here.