[Cs-studio-core] Core plugin change: o.c.platform.libs.epics.linux

[Kasemir, K. <kas...@or...>]

Added filter on osgi.arch=x86 because this plugin will currently not
support x86_64,
i.e. a product will fail to build for x86_64, instead of just omitting
the non-applicable JNI feature.

See
http://cs-studio.hg.sourceforge.net/hgweb/cs-studio/cs-studio-3.1/rev/eb055
fa20826