overo.conf: support meta-ti ti-dsplink builds

Suggestion from http://www.sleepyrobot.com/?p=210 via
http://gumstix.8.n6.nabble.com/gles-and-dsp-support-in-the-official-yocto-layer-tc4965764.html

Signed-off-by: Peter A. Bigot <pab@pabigot.com>
Restrict OMAP3 PWM recipe to Overo.

This PWM driver applies only to OMAP3 platforms like Overo.  The patch
restricts this to Overo so it doesn't get pulled in for DuoVero and
Pepper.
Merge pull request #3 from pabigot/for-dylan/dspbuild

overo.conf: support meta-ti ti-dsplink builds
Add omap3-pwm support to Overo image by default.
Merge branch 'dylan' of git://github.com/gumstix/meta-gumstix into dylan