RISC-V: Move all global static target stuff into private data for disassembler.

RISC-V: Move all global static target stuff into private data for disassembler.

I got a request said that the JDK multi-thread compiler may be broken
if two or more threads are trying to print/disassemble stuff, and filling
the disassemble_info, setting callbacks, and grabbing the function pointer
to disasm at the same time.  Since such as the target global static stuff,
including subset of extensions and mapping symbol stuff, seems to only be
one globally.  Ideally, for dis-assembler, all global static target stuff
should/can be better to be defined into the target private data, since they
are target-dependency.

opcodes/
	* riscv-dis.c: Moved all global static target-dependency stuff into
	riscv_private_data, including architecture and mapping symbol stuff.
	(set_default_riscv_dis_options): Updated since global static target-
	dependency stuff are moved into riscv_private_data.
	(parse_riscv_dis_option_without_args): Likewise.
	(parse_riscv_dis_option): Likewise.
	(parse_riscv_dis_options): Likewise.
	(maybe_print_address): Likewise.
	(print_reg_list): Likewise.
	(riscv_get_spimm): Likewise.
	(print_insn_args): Likewise.
	(riscv_disassemble_insn): Likewise.
	(riscv_update_map_state): Likewise.
	(riscv_search_mapping_symbol): Likewise.
	(riscv_data_length): Likewise.
	(print_insn_riscv): Likewise.  Call the riscv_init_disasm_info before
	parsing any disassembler options, since the related stuff are moved
	into riscv_private_data.
	(riscv_init_disasm_info): Likewise.  Parse and set the architecture
	string and privileged spec version since riscv_get_disassembler is
	no longer needed.
	(riscv_get_disassembler): Removed.
	(disassemble_free_riscv): Only free the subset_list if
	riscv_private_data exsits.
	* disassemble.c (disassembler): Since riscv_get_disassembler is
	removed, call to print_insn_riscv.
	* disassemble.h: Removed extern riscv_get_disassembler.