Switch i.MX to use the platform code to help with a single Freescale kernel.

Differential Revision:	https://reviews.freebsd.org/D1349
Reviewed by:	ian, rpaulo


git-svn-id: svn+ssh://svn.freebsd.org/base/head@276177 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f