MIPS: Netlogic: Add basic MSI support for XLR/XLS

Add basic support for MSI.

Signed-off-by: Ganesan Ramalingam <ganesanr@netlogicmicro.com>
Signed-off-by: Jayachandran C <jayachandranc@netlogicmicro.com>
To: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/2730/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>