[MIPS] Fix the build error of Wind River PPMC board, rewrite irq code to C

 o Fix the build error Wind River PPMC board caused by the change of
   plat_setup hook interface.
 o Rewrite first level interrupt dispatch code to C.

Signed-off-by: Rongkai.Zhan <rongkai.zhan@windriver.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>