fix compilation problem for mpc8349itx CFG_RAMBOOT

fix compilation problem for mpc8349itx CFG_RAMBOOT

Current include/configs/MPC8349ITX.h does contain some support for building
image that will be started from memory (without putting in into flash).
It could be triggered by building with TEXT_BASE set to a low value.

However, this support is incomplete: using of low TEXT_BASE causes
defining configuration macros in inconsistent way, which later leads
to compilation errors. In particular. flash support is being disabled,
but then flash structures get referenced.

This patch fixes this, making it possible to build with low TEXT_BASE.

Signed-Off-By: Nikita Youshchenko <yoush@debian.org>
Signed-off-by: Kim Phillips <kim.phillips@freescale.com>