Add support for R_ARC_NONE relocations.

Add support for R_ARC_NONE relocations.

The R_ARC_NONE relocation is generated when --gc-sections, used by the
compile time linker, removes some sections.  This is completely normal,
and we can see that all other targets (based on random sampling) have
support for R_*_NONE relocations (named for each target).

Handling R_ARC_NONE involves doing nothing with it, which is nice and
easy.

Signed-off-by: Andrew Burgess <andrew.burgess@embecosm.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>