bfd/arc: Add R_ prefix to all relocation names

bfd/arc: Add R_ prefix to all relocation names

The convention within for relocation names is that they start with the
string "R_", however, this is not so for ARC for the display names of
relocations, however, internally, the names for the relocations types do
have the 'R_' prefix.  I suspect that the missing 'R_' on the output
strings was an oversight, as I can't see any comment to the contrary.

To bring ARC into line with other targets, this commit adds the 'R_'
prefix to the output strings used for relocation names, and updates all
of the assembler tests where this was exposed.

bfd/ChangeLog:

	* elf32-arc.c (reloc_type_to_name): Change ARC_RELOC_HOWTO to
	place 'R_' before the reloc name returned.
	(elf_arc_howto_table): Change ARC_RELOC_HOWTO to place 'R_' before
	the relocation string.

gas/ChangeLog:

	* testsuite/gas/arc/adc.d: Add 'R_' prefix to relocation names.
	* testsuite/gas/arc/add.d: Likewise.
	* testsuite/gas/arc/and.d: Likewise.
	* testsuite/gas/arc/asl.d: Likewise.
	* testsuite/gas/arc/asr.d: Likewise.
	* testsuite/gas/arc/bic.d: Likewise.
	* testsuite/gas/arc/extb.d: Likewise.
	* testsuite/gas/arc/extw.d: Likewise.
	* testsuite/gas/arc/j.d: Likewise.
	* testsuite/gas/arc/jl.d: Likewise.
	* testsuite/gas/arc/ld2.d: Likewise.
	* testsuite/gas/arc/lsr.d: Likewise.
	* testsuite/gas/arc/mov.d: Likewise.
	* testsuite/gas/arc/or.d: Likewise.
	* testsuite/gas/arc/pcl-relocs.d: Likewise.
	* testsuite/gas/arc/pcrel-relocs.d: Likewise.
	* testsuite/gas/arc/pic-relocs.d: Likewise.
	* testsuite/gas/arc/plt-relocs.d: Likewise.
	* testsuite/gas/arc/rlc.d: Likewise.
	* testsuite/gas/arc/ror.d: Likewise.
	* testsuite/gas/arc/rrc.d: Likewise.
	* testsuite/gas/arc/sbc.d: Likewise.
	* testsuite/gas/arc/sda-relocs.d: Likewise.
	* testsuite/gas/arc/sda-relocs2.d: Likewise.
	* testsuite/gas/arc/sexb.d: Likewise.
	* testsuite/gas/arc/sexw.d: Likewise.
	* testsuite/gas/arc/st.d: Likewise.
	* testsuite/gas/arc/sub.d: Likewise.
	* testsuite/gas/arc/tls-relocs.d: Likewise.
	* testsuite/gas/arc/xor.d: Likewise.