[POWERPC] Revert "[POWERPC] Add 'mdio' to bus scan id list for platforms with QE UEC"

This reverts commit 3baee955.

That commit was a mistake from the start; I added mdio type to the
bus scan list early on in my ucc_geth migrate to phylib development,
which is just pure wrong (the ucc_geth_mii driver creates the mii
bus and the PHY layer handles PHY enumeration without translation).

This follows on from commit 77926826:

 Revert "[POWERPC] Don't complain if size-cells == 0 in prom_parse()"

which was basically trying to hide a symptom of the original mistake
this revert fixes.

Signed-off-by: Kim Phillips <kim.phillips@freescale.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>