[U-Boot-Users] [MIPS] Make mips_io_port_base more generic

[Shinya Kuribayashi]

Shinya Kuribayashi wrote:
> This patch adds a helper routine for mips_io_port_base from Linux, and fixes
> two multiple definition of this variable, tb0229 and gth2.

I should have fixed all MIPS targets not only tb0229 and gth2. They might
suppose mips_io_port_base is zero, but I change its initial value to -1
in this patch (since Linux does so).

Please don't apply, I'll re-submit later.

Thanks,

    Shinya Kuribayashi