lisa.trace: Use kmod features in FtraceCollector._get_kmods()
lisa.trace: Use kmod features in FtraceCollector._get_kmods()

FEATURE

* Remove support for multiple modules in _get_kmods()
* Use the "features" LISA kmod parameter to enable the events that are
  required and nothing more.

Note that the ftrace events will still be exposed as they are statically
declared, but probe to emit the event will only be registered on the
tracepoint if the feature is enabled. This way, unused events will not
incur any runtime overhead.

ARM-software/lisa,ARM-software/lisa,ARM-software/lisa,ARM-software/lisa