Fix RL78 disassembly so that SP+OFFSET addressing always shows the offset, even when zero.
PR binutils/19157
opcodes * rl78-decode.opc: Add 'a' print operator to mov instructions
using stack pointer plus index addressing.
* rl78-decode.c: Regenerate.
tests * gas/rl78: New directory.
* gas/rl78/rl78.exp: New test driver.
* gas/rl78/pr19157.s: New test source file.
* gas/rl78/pr19157.d: New test case.