powerpc/85xx: workaround for chips with MSI hardware errata

The MPIC version 2.0 has a MSI errata (errata PIC1 of mpc8544), It causes
that neither MSI nor MSI-X can work fine. This is a workaround to allow
MSI-X to function properly.

Signed-off-by: Liu Shuo <soniccat.liu@gmail.com>
Signed-off-by: Li Yang <leoli@freescale.com>
Signed-off-by: Jia Hongtao <hongtao.jia@freescale.com>
Signed-off-by: Scott Wood <scottwood@freescale.com>