Move the cpu_setup() call to the end of initarm(). On Cortex-A53 processors

Move the cpu_setup() call to the end of initarm().  On Cortex-A53 processors
atomic instructions don't work unless the data cache is enabled.  This happens
in cpu_setup(), but that gets currently called from cpu_startup() which runs
after a number of kernel subsystems have been initialized.  Since some of
these subsystems use locks, which need atomic instructions, we fault on
Cortex-A53.  Since at the end of initarm() we're done setting up the pmap
and initializing other low-level sense, calling cpu_setup() here makes much
more sense.

Remove setting up proc0paddr as well from cpu_startup(), since that already
happens in initarm().

Tested on zaurus by deraadt@.

ok jsg@, patrick@