Remove some code duplication in D3D12 (#2144)
Remove some code duplication in D3D12 (#2144)


bkaradzic/bgfx,LWJGL-CI/bgfx,emoon/bgfx,jpcy/bgfx,emoon/bgfx,jdryg/bgfx,bkaradzic/bgfx,jdryg/bgfx,jdryg/bgfx,emoon/bgfx,LWJGL-CI/bgfx,mendsley/bgfx,jpcy/bgfx,mendsley/bgfx,jpcy/bgfx,jpcy/bgfx,jdryg/bgfx,mendsley/bgfx,LWJGL-CI/bgfx,bkaradzic/bgfx,bkaradzic/bgfx,LWJGL-CI/bgfx