kvx bfd signed calculations and _bfd_kvx_elf_resolve_relocation

kvx bfd signed calculations and _bfd_kvx_elf_resolve_relocation

It is generally a good idea to avoid signed arithmetic on values
extracted from object files, to avoid ubsan warnings on overflow.
This patch replaces some uses of bfd_signed_vma in the kvx backend
with bfd_vma, and removes _bfd_kvx_elf_resolve_relocation, a
do-nothing function.  In the process of making this patch I noticed
some dead code in the GOT entry handling, setting value to
got_entry_addr but using "off" in the _bfd_final_link_relocate call.
Since kvx_calculate_got_entry_vma also returns the GOT offset, I
presume the code is correct, but I've left the dead code and comment
there.

	* elfxx-kvx.h (_bfd_kvx_elf_resolve_relocation): Delete.
	* elfxx-kvx.c (kvx_signed_overflow): Rewrite using unsigned
	arithmetic.
	(_bfd_kvx_elf_resolve_relocation): Delete.
	* elfnn-kvx.c (kvx_relocate): Update for
	_bfd_kvx_elf_resolve_relocation removal.
	(elfNN_kvx_final_link_relocate): Likewise.  Don't use a signed
	addend.