cmake: use package-specific prefix in package config helper variable
cmake: use package-specific prefix in package config helper variable

While this isn't a problem in powercap, if packages which depend on
powercap use the same _supported_components variable prior to trying to
find powercap, the variable is overridden and their own component search
might break.

See: https://gitlab.kitware.com/cmake/cmake/-/issues/23112

powercap/powercap,connorimes/powercap