amdgcn: Remove TARGET_GCN5_PLUS

Now that GCN3 support is gone, TARGET_GCN5_PLUS always evaluates to true, so
we can make that code unconditional, and remove all the "else" cases.

The ISA features TARGET_GLOBAL_ADDRSPACE, TARGET_FLAT_OFFSETS,
TARGET_EXPLICIT_CARRY, and TARGET_MULTIPLY_IMMEDIATE, are similarly also
redundant and can be made unconditional.

The naming of the "gcc_version" attribute has been confusing since the "rdna"
attribute was added and this makes it worse, so it has been renamed to "cdna".

The add-with-carry assembler mnemonics no longer have two forms, so '%^' can be
removed.

gcc/ChangeLog:

	* config/gcn/gcn-opts.h (TARGET_GCN5_PLUS): Delete.
	(TARGET_GLOBAL_ADDRSPACE): Delete.
	(TARGET_FLAT_OFFSETS): Delete.
	(TARGET_EXPLICIT_CARRY): Delete.
	(TARGET_MULTIPLY_IMMEDIATE): Delete.
	* config/gcn/gcn-valu.md (*mov<mode>): Rename "gcn_version" to "cdna".
	(*mov<mode>_4reg): Likewise.
	(@mov<mode>_sgprbase): Likwise.
	(gather<mode>_insn_1offset<exec>): Likewise.
	(gather<mode>_insn_1offset_ds<exec>): Likewise.
	(gather<mode>_insn_2offsets<exec>): Likewise.
	(scatter<mode>_insn_1offset<exec_scatter>): Likewise.
	(scatter<mode>_insn_1offset_ds<exec_scatter>): Likewise.
	(scatter<mode>_insn_2offsets<exec_scatter>): Likewise.
	(gather<mode>_insn_1offset<exec>): Remove TARGET_FLAT_OFFSETS
	conditionals.
	(scatter<mode>_insn_1offset<exec_scatter>): Likewise.
	(scatter<mode>_insn_1offset<exec_scatter>): Likewise.
	(add<mode>3<exec_clobber>): Use "_co" instead of "%^".
	(add<mode>3_dup<exec_clobber>): Likewise.
	(add<mode>3_vcc<exec_vcc>): Likewise.
	(add<mode>3_vcc_dup<exec_vcc>): Likewise.
	(addc<mode>3<exec_vcc>): Likewise.
	(sub<mode>3<exec_clobber>): Likewise.
	(sub<mode>3_vcc<exec_vcc>): Likewise.
	(subc<mode>3<exec_vcc>): Likewise.
	(*plus_carry_dpp_shr_<mode>): Likewise.
	(*plus_carry_in_dpp_shr_<mode>): Likewise.
	* config/gcn/gcn.cc (gcn_flat_address_p): Remove TARGET_FLAT_OFFSETS
	conditionals.
	(gcn_addr_space_legitimate_address_p): Likewise.
	(gcn_addr_space_legitimize_address): Likewise.
	(gcn_expand_scalar_to_vector_address): Likewise.
	(print_operand_address): Likewise, and TARGET_GLOBAL_ADDRSPACE also.
	(print_operand): Remove "%^" operand code.
	Remove TARGET_GLOBAL_ADDRSPACE assertion.
	* config/gcn/gcn.h (STACK_ADDR_SPACE): Remove GCN5 conditional.
	* config/gcn/gcn.md (gcn_version): Rename attribute ...
	(cdna): ... to this, and remove the gcn3 and gcn5 values.
	(enabled): Replace old "gcn_version" logic with new "cdna" logic.
	(*mov<mode>_insn): Rename "gcn_version" to "cdna".
	(*movti_insn): Likewise.
	(addsi3): Use "_co" instead of "%^".
	(addsi3_scalar_carry): Likewise.
	(addsi3_scalar_carry_cst): Likewise.
	(addcsi3_scalar): Likewise.
	(addcsi3_scalar_zero): Likewise.
	(addptrdi3): Likewise.
	(subsi3): Likewise.
	(<su>mulsi3_highpart): Remove TARGET_MULTIPLY_IMMEDIATE conditions.
	(<su>mulsi3_highpart_reg): Remove "gcn_version" attribute.
	(muldi3): Likewise.
	(atomic_fetch_<bare_mnemonic><mode>): Likewise.
	(atomic_<bare_mnemonic><mode>): Likewise.
	(sync_compare_and_swap<mode>_insn): Likewise.
	(atomic_load<mode>): Likewise.
	(atomic_store<mode>): Likewise.
	(atomic_exchange<mode>): Likewise.
	(<su>mulsi3_highpart_imm): Remove both TARGET_MULTIPLY_IMMEDIATE and
	"gcn_version".
	(<su>mulsidi3): Likewise.
	(<su>mulsidi3_imm): Likewise.