Add Apple Silicon support

[bobrik]

#161 fixes a crash and a test, but it would be nice to have actual support for Apple Silicon.

$ sysctl machdep.cpu
machdep.cpu.cores_per_package: 8
machdep.cpu.core_count: 8
machdep.cpu.logical_per_package: 8
machdep.cpu.thread_count: 8
machdep.cpu.brand_string: Apple M1

• CPU architecture: aarch64
• Operating System: macOS Big Sur
• Python version: 3.8.8
• Version of py-cpuinfo: 7.0.0

[chadbrewbaker]

This is also barfing under docker. Anyone able to dump /proc/cpuinfo under Ashanti Linux? Based on that it should be a lookup table keyed by machdep.cpu.brand_string.

[thomwiggers]

Dr-Noob/cpufetch#139 contains some information about what sysctl outputs; it seems the cpu flags are fetched differently.