gdb/riscv: Partial support for instructions up to 176-bit

Because riscv_insn_length started to support instructions up to 176-bit,
we need to increase buf size to 176-bit in size.

Also, that would break an assumption in riscv_insn::decode so this commit
fixes it, noting that instructions longer than 64-bit are not fully
supported yet.
1 file changed