MIPS/BFD: Also handle `jalr $0, $25' with R_MIPS_JALR

MIPS/BFD: Also handle `jalr $0, $25' with R_MIPS_JALR

Interpret the `jalr $0, $25' instruction encoding with an R_MIPS_JALR
relocation attached as an alias to `jr $25' and convert the jump to an
equivalent branch where possible, consequently covering the MIPSr6
architecture for the purpose of this optimization too.

	bfd/
	* elfxx-mips.c (mips_elf_perform_relocation): Also handle the
	`jalr $0, $25' instruction encoding.

	gas/
	* testsuite/gas/mips/jalr4.s: Add `jalr $0, $25' instructions.
	* testsuite/gas/mips/jalr4.d: Adjust accordingly.  Remove MIPSr6
	encoding patterns.
	* testsuite/gas/mips/jalr4-n64.d: Likewise.
	* testsuite/gas/mips/mipsr6@jalr4.d: New test.
	* testsuite/gas/mips/mipsr6@jalr4-n32.d: New test.
	* testsuite/gas/mips/mipsr6@jalr4-n64.d: New test.

	ld/
	* testsuite/ld-mips-elf/jalr4.dd: Adjust for `jalr $0, $25'
	instructions.
	* testsuite/ld-mips-elf/jalr4-r6.dd: New test.
	* testsuite/ld-mips-elf/mips-elf.exp: Run the new test.