radeonsi: increase performance for DRI PRIME offloading if 2nd GPU is CIK or VI

radeonsi: increase performance for DRI PRIME offloading if 2nd GPU is CIK or VI

SDMA is much faster for tiled->linear blits from VRAM to GTT.
I have Bonaire in my second PCIe slot.

$ glxinfo | grep OpenGL.renderer
OpenGL renderer string: Gallium 0.4 on AMD TONGA ...

$ DRI_PRIME=1 glxinfo | grep OpenGL.renderer
OpenGL renderer string: Gallium 0.4 on AMD BONAIRE ...

Without SDMA:
$ DRI_PRIME=1 glxgears
8796 frames in 5.0 seconds = 1759.074 FPS
8899 frames in 5.0 seconds = 1779.672 FPS

With SDMA:
$ DRI_PRIME=1 glxgears
12765 frames in 5.0 seconds = 2552.788 FPS
12888 frames in 5.0 seconds = 2577.495 FPS

The 1st GPU is irrelevant. The improvement should be much lower at 60 fps,
but definitely measurable.

SI will get this once we add SDMA blit support for it.

Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>