Move ofw_cpu.c to sys/dev/ofw so that it can be used by other
architectures.

Differential Revision:	https://reviews.freebsd.org/D1307
Reviewed by:	jhibbits


git-svn-id: svn+ssh://svn.freebsd.org/base/head@275779 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f