[armv7] dtb specified with FDT_DTS_FILE in kernconf not built when using release.sh

Hi,

I'm trying to cross-build (from amd64) a custom -CURRENT armv7 image for 
my beaglebone enhanced using the release(7) method with a custom 
release.conf script, which I wrote starting from release/arm/GENERICSD.

The only customization that I want to include is to use the appropriate 
dtb compiled from the dts files for this board. I thought I could 
achieve this goal by having "makeoptions FDT_DTS_FILE=..." in my 
kernconf, but the dtb does not seem to be compiled in the chrootdir, not 
to say installed, the image.

The kernconf is the following:

include GENERIC
include "../../conf/std.nodebug"
ident   GENERIC-ND-BBE
makeoptions FDT_DTS_FILE=am335x-sancloud-bbe.dts

My release.conf script has a custom buildenv_setup() function to cp the
above kernconf to the /usr/src/sys/arm/conf/ directory of the chroot, 
and the dts to /usr/src/sys/dts/arm of the chroot (from what I could 
infer, that is the correct path for the dts, but please let me know if 
that's not the case).

I don't see the compiled dtb anywhere in the chroot, nor an error 
message or a warning that it failed to build, and it is not in the image 
either.

What am I missing?

Thanks,
Matteo