* config/rs6000/rs6000.md (floatsidf2_internal): Merge to create
define_insn_and_split. Split only when memory operand is
offsettable. Use adjust_address rather than plus_constant.
(floatunssidf2_internal): Likewise.
(fix_truncdfsi2_internal): Split only when memory operand is
offsettable. Use adjust_address rather than plus_constant.
(fix_trunctfsi2_internal): Likewise.
(floatsidf2_internal): Likewise.