Fix the V850 assembler's generation of relocations for the st.b instruction.

	PR 28292
gas	* config/tc-v850.c (handle_lo16): Also accept
	BFD_RELOC_V850_LO16_SPLIT_OFFSET.
	* testsuite/gas/v850/split-lo16.s: Add extra line.
	* testsuite/gas/v850/split-lo16.d: Update expected disassembly.

opcodes	* v850-opc.c (D16): Use BFD_RELOC_V850_LO16_SPLIT_OFFSET in place
	of BFD_RELOC_16.