powerpc: make Freescale QE support a selectable Kconfig option

Modify the Kconfig so that Freescale QUICC Engine (QE) support is a selectable
option, thereby allowing users to compile kernels without any QE support.

The drawback is that QE support is now disabled by default on platforms that
have a QE, and so a defconfig is needed to enable QE and QE devices (like
UCC GETH).  Fortunately, all the current relevant defconfigs do that already.

Signed-off-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>