Add prefetch configuration to aarch64 backend.

Add prefetch configuration to aarch64 backend.

	* config/aarch64/aarch64-protos.h (struct cpu_prefetch_tune):
	New tune structure.
	(struct tune_params): Use cpu_prefetch_tune instead of cache_line_size.
	[Unrelated to main purpose of the patch] Place the pointer field last
	to enable type checking errors when tune structure are wrongly merged.
	* config/aarch64/aarch64.c (generic_prefetch_tune,)
	(exynosm1_prefetch_tune, qdf24xx_prefetch_tune,)
	(thunderx2t99_prefetch_tune): New tune constants.
	(tune_params *_tunings): Update all tunings (no functional change).
	(aarch64_override_options_internal): Set PARAM_SIMULTANEOUS_PREFETCHES,
	PARAM_L1_CACHE_SIZE, PARAM_L1_CACHE_LINE_SIZE, and PARAM_L2_CACHE_SIZE
	from tunings structures.

Change-Id: I1ddbac1863dcf078a2e5b14dd904debc76a7da94

From-SVN: r249240