target/riscv: Remove unnecessary riscv_*_names[] declaration

target/riscv: Remove unnecessary riscv_*_names[] declaration

riscv_excp_names[] and riscv_intr_names[] are only referenced by
target/riscv/cpu.c locally.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 20210514052435.2203156-1-bmeng.cn@gmail.com
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>