FreeBSD_HEAD_i386 - Build #2353 - Fixed

FreeBSD_HEAD_i386 - Build #2353 - Fixed:

Build information: https://jenkins.FreeBSD.org/job/FreeBSD_HEAD_i386/2353/
Full change log: https://jenkins.FreeBSD.org/job/FreeBSD_HEAD_i386/2353/changes
Full build log: https://jenkins.FreeBSD.org/job/FreeBSD_HEAD_i386/2353/console

Change summaries:

295663 by bdrewery:
Revert r295648 for now.

This builds fine with FAST_DEPEND but the mkdep method requires that
include/ generates the headers during 'make depend' so the subsequent
directories can find them when running mkdep.

Sponsored by:	EMC / Isilon Storage Division

295662 by andrew:
Allow callers of OF_decode_addr to get the size of the found mapping. This
will allow for code that uses the old fdt_get_range and fdt_regsize
functions to find a range, map it, access, then unmap to replace this, up
to and including the map, with a call to OF_decode_addr.

As this function should only be used in the early boot code the unmap is
mostly do document we no longer need the mapping as it's a no-op, at least
on arm.

Reviewed by:	jhibbits
Sponsored by:	ABT Systems Ltd
Differential Revision:	https://reviews.freebsd.org/D5258