I agree with you that a way to get a quick list of codecs, resolutions, etc. supported by the combination of HW, OS, driver, and Media SDK version would be very helpful. It's possible now if your application includes some tests but there will be more to it than a single function call.
1) attempt to load the plugin. If this fails HEVC isn't available.
2) set up the mfxVideoParam settings for an HEVC encode then use MFXVideoENCODE_Query or MFXVideoENCODE_Init. If any warnings or errors assume the HW HEVC codec isn't available.
You could also check the processor architecture in your application to make sure it is at least 6th Generation Core/Skylake. There is also no Media SDK function for this, but there are many alternative paths to get this info.
If your app checks the processor and finds the appropriate architecture but the other tests fail you could offer a helpful message to check that the driver is updated to the latest version available.
Hope this helps,