irqchip/ls-scfg-msi: Add LS1012a MSI support

The ls1012a implements only 1 MSI controller, and it is the same as
ls1043a.

Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Minghuan Lian <minghuan.Lian@nxp.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>