Fix copy-paste error in src/cpu/x86/Kconfig.

Fix copy-paste error in src/cpu/x86/Kconfig.

That file defines XIP_ROM_BASE twice, but the latter definition should
be XIP_ROM_SIZE (not *_BASE).

These exact two definitions are listed in src/Kconfig already, though,
so maybe one of the two locations should remove them?

Signed-off-by: Uwe Hermann <uwe@hermann-uwe.de>
Acked-by: Stefan Reinauer <stepan@coresystems.de>
git-svn-id: svn://svn.coreboot.org/coreboot/trunk@4571 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1