powercap: intel_rapl: Use bitmap for Power Limits

Currently, a RAPL package is registered with the number of Power Limits
supported in each RAPL domain. But this doesn't tell which Power Limits
are available. Using the number of Power Limits supported to guess the
availability of each Power Limit is fragile.

Use bitmap to represent the availability of each Power Limit.

Note that PL1 is mandatory thus it does not need to be set explicitly by
the RAPL Interface drivers.

No functional change intended.

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Tested-by: Wang Wendy <wendy.wang@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>