net: ethernet: freescale: make UCC_GETH explicitly depend on PPC32

Currently, QUICC_ENGINE depends on PPC32, so this in itself does not
change anything. In order to allow removing the PPC32 dependency from
QUICC_ENGINE and avoid allmodconfig build failures, add this explicit
dependency.

Also, the QE Ethernet has never been integrated on any non-PowerPC SoC
and most likely will not be in the future.

Reviewed-by: Timur Tabi <timur@kernel.org>
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Li Yang <leoyang.li@nxp.com>