sparc64: Fix SMP bootup with CONFIG_STACK_DEBUG or ftrace.

Based upon a report by Meelis Roos.

Any function call can try to access the current
thread register via the _mcount hooks when the kernel
is built with -pg (via ftrace or STACK_DEBUG).

That can't be setup properly very early on during
the bootup of other cpus for sun4u and some early
sun4v systems.

So add notrace markers to these specific functions, so
that _mcount doesn't get invoked too early.

Signed-off-by: David S. Miller <davem@davemloft.net>