Don't define RISC-V .p2align

Don't define RISC-V .p2align

	* config/tc-riscv.c (riscv_pseudo_table): Remove "align",
	"p2align", and "balign".
	(s_align): Remove.
	(riscv_handle_align): New function.
	(riscv_frag_align_code): Likewise.
	(riscv_make_nops): Likewise.
	* config/tc-riscv.h (MAX_MEM_FOR_RS_ALIGN_CODE): Change to 7.
	(HANDLE_ALIGN): Define.
	(md_do_align): Define.
	(riscv_handle_align): Declare.
	(riscv_frag_align_code): Likewise.