Radeon KMS On PC-BSD/FreeBSD 10.2 Surprisingly Worked On A FirePro+DP System

While open-source AMD Linux users have largely been able to take it for granted for years that the Radeon DRM/KMS driver will at least light up their display when using an older GPU, after the Radeon KMS problems I ran into on DragonFlyBSD, I didn't expect this hardware to play nicely on FreeBSD/PC-BSD 10.2. Fortunately, I was proven wrong and this AMD FirePro graphics card driving a DisplayPort monitor managed to run nicely out-of-the-box...