tests: Fix compilation of cprinftest.

tests: Fix compilation of cprinftest.

This test has been broken since 70176fecd1ff04 in 2014. The problem was
that the array size in the test was technically not constant because it
was based on an int variable that wasn't declared as const. That
prevented g++ from resolving it as a template parameter. Before the
change mentioned above, the implementation wasn't based on templates.

Change-Id: I6819cf522f9ba4636ac661da368b9bcbae0a813f
Reviewed-on: https://gem5-review.googlesource.com/5821
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>