MIPS: MT: Mark existing TCs as present

According to Documentation/cpu-hotplug.txt, the cpu_present_mask should
contain all the CPUs which are present in the system. Therefore, all the TCs
currently present in the system should be marked as 'present' even if they
will never be brought online.

Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Signed-off-by: John Crispin <blogic@openwrt.org>
Patchwork: http://patchwork.linux-mips.org/patch/6039/