sparc: Treat more instructions as load or store in errata workarounds

Check the attribute of instruction to determine if it performs a store
or load operation. This more generic approach sees the last instruction
in the GOTdata_op model as a potential load and treats the memory barrier
as a potential store instruction.

gcc/ChangeLog:

	* config/sparc/sparc.c (store_insn_p): Add predicate for store
	attributes.
	(load_insn_p): Add predicate for load attributes.
	(sparc_do_work_around_errata): Use new predicates.