ARM: LPC32xx: Remove SLC controller initialization from platform init

Since we now support two MTD NAND controllers (MLC and SLC) for LPC32xx via DT,
we don't initialize the SLC controller statically anymore, but do it via the
clock setup (see previous patch).

Signed-off-by: Roland Stigge <stigge@antcom.de>
Tested-by: Alexandre Pereira da Silva <aletes.xgr@gmail.com>