trinity: enable only for supported architectures

This package only has support for some architectures which are listed in
the project website: http://codemonkey.org.uk/projects/trinity/

We enable this package only for those supported architectures which are
also supported in Buildroot.

Fixes:
	http://autobuild.buildroot.net/results/ea7/ea788f1f0ed5ee4e9b1bf0c8a0d1304e7467dc77/



Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>