CPU feature checking - require ARMv8

 The packages in the isa-support family probe for microprocessor Instruction
 Set Architecture features such as SSE3. By refusing to install on machines
 lacking a required feature, they allow ISA requirements to be handled in
 terms of package dependencies.
 .
 This is a mostly dummy package which checks for ARMv8 and refuses to install
 on unsupported hardware.
 .
 ARMv8 (not to be confused with product family ARM8) introduced a large
 number of ISA enhancements. It is not guaranteed by the architecture
 baseline, but is available for newer armel machines (including CPUs that
 support armhf) since the Cortex-A product family, including Cortex-A32, as
 well as all arm64 processors. Boards include the Raspberry Pi 3 and 4.