powerpc/8xx: Convert CPM1 interrupt controller to platform_device

In the same logic as commit be7ecbd2 ("soc: fsl: qe: convert QE
interrupt controller to platform_device"), convert CPM1 interrupt
controller to platform_device.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/fb80d0b2077312079c49da0296e25591578771cd.1649226186.git.christophe.leroy@csgroup.eu