mpc8313e-rdb: Merge Freescale's patches for u-boot 1.2.0 and linux 2.6.24.3.

mpc8313e-rdb: Merge Freescale's patches for u-boot 1.2.0 and linux 2.6.24.3.
Also make the u-boot version set conditionally rather than unconditionally,
in the machine configuration file.
Although u-boot 1.2.0 and 2.6.24.3 are reasonably outdated, the PCI Express
support has never been merged upstream, neither to u-boot nor to linux, so
use the above versions if you want to toy with PCI Express.
It was extracted from MPC8315ERDB_20080627-ltib.iso, of which the patches
are also available online at www.bitshrine.org.