After removing `get_runtime_isa`, the `send_evicts` function in the ruby
configs assumes that there is an ISA built. This change short-circuits
that logic if the current build is the NULL (none) ISA.
Change-Id: I75fefe3d70649b636b983c4d2145c63a9e1342f7
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>