[AArch64] Track FP registers in prologue analyzer

[AArch64] Track FP registers in prologue analyzer

We don't track FP registers in aarch64 prologue analyzer, so this causes
an internal error when FP registers are saved by "stp" instruction in
prologue (stp	d8, d9, [sp,#128]),

 tbreak _Unwind_RaiseException^M
 aarch64-tdep.c:335: internal-error: CORE_ADDR aarch64_analyze_prologue(gdbarch*, CORE_ADDR, CORE_ADDR, aarch64_prologue_cache*): Assertion `inst.operands[0].type == AARCH64_OPND_Rt' failed.^M
 A problem internal to GDB has been detected,

This patch teaches GDB to track FP registers (D registers) in prologue
analyzer.

gdb:

2016-10-12  Yao Qi  <yao.qi@linaro.org>

	PR tdep/20682
	* aarch64-tdep.c: Replace 32 with AARCH64_D_REGISTER_COUNT.
	(aarch64_analyze_prologue): Extend array 'regs' for D registers.
	Assert that operand 0 and 1 can be X or D registers.  Update
	register number for D registers.  Update registers in frame
	cache.
	* aarch64-tdep.h (AARCH64_D_REGISTER_COUNT): New macro.