Refactor Nios II GDB support to use helper functions for disassembly and

Refactor Nios II GDB support to use helper functions for disassembly and
instruction matching.

2014-11-25  Sandra Loosemore  <sandra@codesourcery.com>

	gdb/
	* nios2-tdep.c (nios2_fetch_insn): Move up in file.  Disassemble
	the instruction as well as reading it from memory.
	(nios2_match_add): New.
	(nios2_match_sub): New.
	(nios2_match_addi): New.
	(nios2_match_orhi): New.
	(nios2_match_stw): New.
	(nios2_match_ldw): New.
	(nios2_match_rdctl): New.
	(enum branch_condition): New.
	(nios2_match_branch): New.
	(nios2_match_jmpi): New.
	(nios2_match_calli): New.
	(nios2_match_jmpr): New.
	(nios2_match_callr): New.
	(nios2_match_break): New.
	(nios2_match_trap): New.
	(nios2_in_epilogue_p): Rewrite to use new functions.
	(nios2_analyze_prologue): Likewise.
	(nios2_skip_prologue): Delete unused local limit_pc.
	(nios2_breakpoint_from_pc): Make R1-specific encodings explicit.
	(nios2_get_next_pc): Rewrite to use new functions.