consolidate definition of CPU features

While porting JDK-8224974 to Graal, I noticed that new CPU features were defined for x86[1] and AArch64. However, these features were not exposed via JVMCI. To avoid this problem in future, CPU features could be defined by a single macro that can be used to generate enum declarations as well as vmstructs entries.

[1]: https://github.com/openjdk/jdk/commit/047b8bfeb73d00ebf9675520f7a4c085e514e050#diff-1537a167a92a2fbcf8820a494962154dadb282f815e98c0598466041381f0809R345-R347