[Bug target/64659] [SH] Immedate values not used for atomic ops

[olegendo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64659

--- Comment #2 from Oleg Endo <olegendo at gcc dot gnu.org> ---
The other issue is that atomic add insns for models other than 'hard-llcs' do
not utilize the 'add #imm,Rn' insn at all, because those insns allow
'register_operand' only.