aarch64: Add costs for LD[34] and ST[34] postincrements

aarch64: Add costs for LD[34] and ST[34] postincrements

Most postincrements are cheap on Neoverse V1, but it's
generally better to avoid them on LD[34] and ST[34] instructions.
This patch adds separate address costs fields for these cases.
Other CPUs continue to use the same costs for all postincrements.

gcc/
	* config/aarch64/aarch64-protos.h
	(cpu_addrcost_table::post_modify_ld3_st3): New member variable.
	(cpu_addrcost_table::post_modify_ld4_st4): Likewise.
	* config/aarch64/aarch64.c (generic_addrcost_table): Update
	accordingly, using the same costs as for post_modify.
	(exynosm1_addrcost_table, xgene1_addrcost_table): Likewise.
	(thunderx2t99_addrcost_table, thunderx3t110_addrcost_table):
	(tsv110_addrcost_table, qdf24xx_addrcost_table): Likewise.
	(a64fx_addrcost_table): Likewise.
	(neoversev1_addrcost_table): New.
	(neoversev1_tunings): Use neoversev1_addrcost_table.
	(aarch64_address_cost): Use the new post_modify costs for CImode
	and XImode.