tools/power/x86/intel-speed-select: Introduce is_debug_enabled()

Platform specific code also needs to give debug output.
Introduce is_debug_enabled() for this purpose.

No functional changes are expected.

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
[srinivas.pandruvada@linux.intel.com: changelog edits]
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>