cpu: refactor parsing of ARM64 registers into separate function
cpu: refactor parsing of ARM64 registers into separate function

This will allow to re-use the implementation when adding support for
netbsd/arm64 which will retreive these register values using sysctl(3).

Change-Id: I2414cc4c6d1a91fff946466e4bf6d95d07f30137
Reviewed-on: https://go-review.googlesource.com/c/sys/+/264377
Trust: Tobias Klauser <0a68dd4915066ec5d3f81f75a828fee53dcc8822@gmail.com>
Run-TryBot: Tobias Klauser <0a68dd4915066ec5d3f81f75a828fee53dcc8822@gmail.com>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Martin Möhrmann <9c82b83f348009b39856043bb9ed3ef41e171aeb@google.com>

golang/sys,golang/sys,golang/sys