[rtl818x] Remove broken mmio register support

[rtl818x] Remove broken mmio register support

The rtl818x driver uses programmed I/O but has a fallback to
memory-mapped I/O registers.  The fallback currently will not work since
the registers are accessed using inl()/outl() programmed I/O functions
in the driver.  This patch removes the fallback to we fail cleanly when
programmed I/O is not possible.

Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
Signed-off-by: Joshua Oreman <oremanj@rwcr.net>
Signed-off-by: Marty Connor <mdc@etherboot.org>