RISC-V: Use riscv_subword_address for atomic_test_and_set

RISC-V: Use riscv_subword_address for atomic_test_and_set

Other subword atomic patterns use riscv_subword_address to calculate
the aligned address, shift amount, mask and !mask. atomic_test_and_set
was implemented before the common function was added. After this patch
all subword atomic patterns use riscv_subword_address.

gcc/ChangeLog:

	* config/riscv/sync.md:  Use riscv_subword_address function to
	calculate the address and shift in atomic_test_and_set.

Signed-off-by: Patrick O'Neill <patrick@rivosinc.com>