ARM memory layout fixes: the abort-stack is now set up in the
correct RAM area, and the BSS is zeroed out as it should be.
Furthermore, the magic variables 'armboot_end' and 'armboot_end_data'
of the linker scripts are replaced by '__bss_start' and '_end',
resp., which is a further step to eliminate unnecessary differences
between the implementation of the CPU architectures.
Move most of the timer interrupt related PPC code to ppc_lib/interrupts.c
* Patch by Anders Larsen, 17 Sep 2003:
Bring ARM memory layout in sync with the documentation:
stack and malloc-heap are now located _below_ the U-Boot code
