RISC-V/testsuite: Restrict remaining `fmin'/`fmax' tests to hard float

RISC-V/testsuite: Restrict remaining `fmin'/`fmax' tests to hard float

Complement commit 7915f6551343 ("RISC-V/testsuite: constraint some of
tests to hard_float") and also restrict the remaining `fmin'/`fmax'
tests to hard-float test configurations.

	gcc/testsuite/
	* gcc.target/riscv/fmax-snan.c: Add `dg-require-effective-target
	hard_float'.
	* gcc.target/riscv/fmaxf-snan.c: Likewise.
	* gcc.target/riscv/fmin-snan.c: Likewise.
	* gcc.target/riscv/fminf-snan.c: Likewise.