Code review comment for lp:~andreas-pokorny/mir/pixel-format-utils

I still have reservations that "deduplicating the pixel format types" was the right thing to do. We had a c-compatible pixel format and an internal pixel format class whose intention was to be more versatile and have functions on the formats to check the alpha capabilities, color depths, etc.
However, those reservations shouldn't block this review. Looks okay to me