Saw this here, which is an article about a Phronix article speculating on the large code commit for the open AMD drivers.
Link: AMD publishes patches for Vega support on Linux
Link: AMD publishes patches for Vega support on Linux
As Phoronix speculates, the amount of code might owe to the fact that Vega is a significant departure from the previous Polaris architecture. The site says that the patches include support for video decoding using Vega's UVD 7.0 decode block, video encoding using VCE 4.0, and support for SR-IO virtualization alongside the more basic power management and 3D graphics functions.