Add Power 10 PLT instruction patterns

Add Power 10 PLT instruction patterns

gdb/ChangeLog:

2021-06-07  Carl Love  <cel@us.ibm.com>

	* ppc-tdep.h (ppc_insn_prefix_dform): Declare.
	* ppc64-tdep.c(insn_md, insn_x, insn_xo): New macros.
	(ppc64_plt_pcrel_entry_point, ppc64_pcrel_linkage1_target,
	ppc64_pcrel_linkage2_target): New functions.
	(ppc64_standard_linkage9, ppc64_standard_linkage10,
	ppc64_standard_linkage11, ppc64_standard_linkage12): New ppc
	instruction patterns.
	(ppc64_standard_linkage9, ppc64_standard_linkage10,
	ppc64_standard_linkage11, ppc64_standard_linkage12): New variables
	in define MAX expression.
	(ppc64_skip_trampoline_code_1): Handle ppc64_standard_linkage9,
	ppc64_standard_linkage10, ppc64_standard_linkage11,
	ppc64_standard_linkage12.
	* (ppc_insn_prefix_dform): New function.