nds32: Fill all TLB entries with kernel image mapping

We use earlycon replace with early_printk and doesn't use
early_io_map() to create UART mapping. It is not necessary
to reserve the one way in TLB for now.

It didn't make sense if use direct-mapped and reserve one
way at the same time. It allow the direct-mapped now.

Signed-off-by: Zong Li <zong@andestech.com>
Signed-off-by: Greentime Hu <greentime@andestech.com>