There is no dtb file in http://autobuilder.yoctoproject.org/pub/nightly/20130327-1/machines/mpc8315e-rdb/ . But it exists in http://autobuilder.yoctoproject.org/pub/nightly/20130327-1/machines/qemu/qemuppc/ I also found some kernel and rootfs for real hardware BSPS are in machines/qemu direcotry. For example, the routerstationpro kernel and rootfs exist in machines/qemumips directory and atom-pc kernel and rootfs exist in machines/qemux86 directory.
d10fcb2291bd5982abe8a27bea151e25736b74c7 and 1142f58a2df93c7d556d7b2051653da555658f25 should fix this.
The dtb file is still missing in current weekly test build: http://autobuilder.yoctoproject.org/pub/nightly/20130403-2/machines/mpc8315e-rdb/ And the lasted build: http://autobuilder.yoctoproject.org/pub/nightly/20130406-2/machines/mpc8315e-rdb/ is also missing this file.
Fixed in http://git.yoctoproject.org/cgit/cgit.cgi/yocto-autobuilder/commit/?h=eflanagan/yocto-autobuilder-refactor&id=19bccb80383ff92cba0cc7b89df766f26012b7cb