AArch64: kernel events included by default

On current kernels the format of /proc/cpuinfo is different from what linux-common.c is expecting. It doesn't detect the architecture revision, and this causes a workaround for old core bugs in perf_event.c to default to including the kernel, when normally we'd only monitor userspace. A simple fix is to update linux-common.c to handle the newer format of /proc/cpuinfo as well as the old one.

I've created a pull request for this.