powerpc: Build-in e1000e for pseries & ppc64_defconfig

The e1000e device is becoming more common these days, so let's just
build it in for pseries & ppc64_defconfig.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>