RISC-V: Don't generate the ELF privilege attributes when no CSR are used.

RISC-V: Don't generate the ELF privilege attributes when no CSR are used.

	gas/
	* config/tc-riscv.c (explicit_csr): New static boolean.
	Used to indicate CSR are explictly used.
	(riscv_ip): Set explicit_csr to TRUE if any CSR is used.
	(riscv_write_out_attrs): If we already have set elf priv
	attributes, then generate them.  Otherwise, don't generate
	them when no CSR are used.

	* testsuite/gas/riscv/attribute-01.d: Remove the priv attributes.
	* testsuite/gas/riscv/attribute-02.d: Likewise.
	* testsuite/gas/riscv/attribute-03.d: Likewise.
	* testsuite/gas/riscv/attribute-04.d: Likewise.
	* testsuite/gas/riscv/attribute-05.d: Likewise.
	* testsuite/gas/riscv/attribute-06.d: Likewise.
	* testsuite/gas/riscv/attribute-07.d: Likewise.
	* testsuite/gas/riscv/attribute-08.d: Likewise.
	* testsuite/gas/riscv/attribute-09.d: Likewise.
	* testsuite/gas/riscv/attribute-10.d: Likewise.
	* testsuite/gas/riscv/attribute-unknown.d: Likewise.
	* testsuite/gas/riscv/attribute-11.s: New testcase.
	* testsuite/gas/riscv/attribute-11.d: New testcase.  The CSR is
	used, so we should output the ELF priv attributes.
	* testsuite/gas/riscv/attribute-12.d: New testcase.  The CSR is
	used, so output the priv attributes according to the -mpriv-spec.
	* testsuite/gas/riscv/attribute-13.d: New testcase.  The CSR isn't
	used, so ignore the -mpriv-spec setting.

	ld/
	* testsuite/ld-riscv-elf/attr-merge-arch-01.d: Likewise.
	* testsuite/ld-riscv-elf/attr-merge-arch-02.d: Likewise.
	* testsuite/ld-riscv-elf/attr-merge-arch-03.d: Likewise.
	* testsuite/ld-riscv-elf/attr-merge-stack-align.d: Likewise.
	* testsuite/ld-riscv-elf/attr-merge-strict-align-01.d: Likewise.
	* testsuite/ld-riscv-elf/attr-merge-strict-align-02.d: Likewise.
	* testsuite/ld-riscv-elf/attr-merge-strict-align-03.d: Likewise.
	* testsuite/ld-riscv-elf/attr-merge-strict-align-04.d: Likewise.
	* testsuite/ld-riscv-elf/attr-merge-strict-align-05.d: Likewise.
	* testsuite/ld-riscv-elf/call-relax.d: Add -mno-arch-attr.