oprofile/mips: override register writes for qemu mips 64

Even when oprofile timer mode is enabled, during oprofile arch init
there are writes to registers that do not exist in the qemu malta
64 bit pseudo machine.

To allow initialization to continue and the fallback to oprofile
timer mode to take effect, we stub the register writes.

These two defines are only appropriate for qemu-system-mips.
This should not merge to a common location, and only be applied
to emulated boards.

Signed-off-by: Bruce Ashfield <bruce.ashfield@windriver.com>