mips: Use generic init_task

Same code. Use the generic version. The special Makefile treatment is
pointless anyway as init_task.o contains only data which is handled by
the linker script. So no point on being treated like head text.

Make the linker script align the task on THREAD_SIZE and not on
PAGE_SIZE, as PAGE_SIZE might be smaller than THREAD_SIZE.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Ralf Baechle <ralf@linux-mips.org>
Link: http://lkml.kernel.org/r/20120503085034.941344764@linutronix.de