ARM: kprobes: Fix test code compilation errors for ARMv4 targets

Conditionally compile kprobes test cases for ARMv5 instructions to avoid
compilation errors with ARMv4 targets like:

/tmp/cc7Tx8ST.s:16740: Error: selected processor does not support ARM mode `clz r0,r0'

Signed-off-by: Jon Medhurst <tixy@linaro.org>