rtla: Enable use of libcpupower
rtla can use libcpupower to disable idle states for better real-time behaviour, but currently it doesn't detect that libcpupower is available.
- d/rules.real: Make building rtla depend on building cpupower
- d/rules.d/tools/power/libcpupower: Add the required compiler and linker options to enable detection and use of the just- built libcpupower