opcodes/riscv: implement style support in the disassembler

opcodes/riscv: implement style support in the disassembler

Update the RISC-V disassembler to supply style information.  This
allows objdump to apply syntax highlighting to the disassembler
output (when the appropriate command line flag is used).

Ignoring colours, there should be no other user visible changes in the
output of the disassembler in either objdump or gdb.

opcodes/ChangeLog:

	* disassembler.c (disassemble_init_for_target): Set
	created_styled_output for riscv.
	* riscv-dis.c: Changed throughout to use fprintf_styled_func
	instead of fprintf_func.