staging: fsl-mc: Convert to use platform_msi infrastrucutre

[Matthias Brugger]

Freescale MC driver can't be build as module as it uses it's own
msi implementation. This patch set converts the driver to use platform_msi
infrastructure instead, so that we can build the driver as a module.

Apart from that we have to export some functions of the msi framework to
handle the domain.