ppc4xx: Fix misspelled CONFIG_440SPE/440EPX/GRX config options

We use upper case letters for the AMCC processor defines (like
CONFIG_440SPE) in U-Boot. So the 440SPe is labeled CONFIG_440SPE and
not CONFIG_440SPe. This patch fixes the last misspelled config options.

Signed-off-by: Stefan Roese <sr@denx.de>