hw/riscv: microchip_pfsoc: Connect the IOSCB module

hw/riscv: microchip_pfsoc: Connect the IOSCB module

Previously IOSCB_CFG was created as an unimplemented device. With
the new IOSCB model, its memory range is already covered by the
IOSCB hence remove the previous unimplemented device creation in
the SoC codes.

Signed-off-by: Bin Meng <bin.meng@windriver.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 1603863010-15807-6-git-send-email-bmeng.cn@gmail.com
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>