add events.h for Cortex-A35

[axel-h]

seL4/seL4@5b611a0 from @bennoleslie added basic support for the Cortex-A35. We need a libsel4bench/arch_include/arm/cpu/cortex-a35/sel4bench/cpu/events.h then also.
Maybe we can just copy the Cortex A72 file that #27 adds.
Note that as long as libsel4bench is not used on an Cortex-A35 platform, there is no problem. However, when using the CAmkES global components, one can't cherry-pick things there. BenchUtiliz is always built (even if not used) and this pulls in libsel4bench then, which triggers an error then that the file is missing.