Add powerpc feature detection & double/int64 support
This re-adds the cpu feature detection on PowerPC & adds support for double/int64 opcodes.
- Fixes meson build to compile cpu detection
- Extended the linux detection to detect VSX extensions, v2.07 architecture, cache sizes & cpu type
- Add support to display flag names
- Adds opcode support for double & int64 if VSX/v2.07 is detected