aarch64: Move more code into aarch64_vector_costs

aarch64: Move more code into aarch64_vector_costs

This patch moves more code into aarch64_vector_costs and reuses
some of the information that is now available in the base class.

I'm planing to significantly rework this code, with more hooks
into the vectoriser, but this seemed worth doing as a first step.

gcc/
	* config/aarch64/aarch64.c (aarch64_vector_costs): Make member
	variables private and add "m_" to their names.  Remove is_loop.
	(aarch64_record_potential_advsimd_unrolling): Replace with...
	(aarch64_vector_costs::record_potential_advsimd_unrolling): ...this.
	(aarch64_analyze_loop_vinfo): Replace with...
	(aarch64_vector_costs::analyze_loop_vinfo): ...this.
	Move initialization of (m_)vec_flags to add_stmt_cost.
	(aarch64_analyze_bb_vinfo): Delete.
	(aarch64_count_ops): Replace with...
	(aarch64_vector_costs::count_ops): ...this.
	(aarch64_vector_costs::add_stmt_cost): Set m_vec_flags,
	using m_costing_for_scalar to test whether we're costing
	scalar or vector code.
	(aarch64_adjust_body_cost_sve): Replace with...
	(aarch64_vector_costs::adjust_body_cost_sve): ...this.
	(aarch64_adjust_body_cost): Replace with...
	(aarch64_vector_costs::adjust_body_cost): ...this.
	(aarch64_vector_costs::finish_cost): Use m_vinfo instead of is_loop.