Deprecate default as cov option

[ellosel]

If users are configuring with cmake directly and explicitly set cov to "default" this will change default to 4 and warn that the default option is deprecated.

[bstefanuk]

I'm concerned this won't cover all of the use-cases (though it may). Some individuals are setting code object version in input configuration files, so they may be looking for a way to translate those entries internal to Tensile/TensileCreateLibrary. We may have to hunt down these workflows for more clarity.