fp16 support in xBGR order, and for DCE-11+

[Mario Kleiner]

Hi,

two patches. The first one adds the xBGR ordered variants of fp16
in addition to the xRGB ordered variants that were merged just
very recently.

These variants are required for direct scanout of OpenGL and Vulkan
rendered content, as both OpenGL (GL_RGBA16F) and Vulkan
(VK_FORMAT_R16G16B16A16_SFLOAT) expect RGBA channel order for fp16,
instead of the previously exposed BGRA fp16 ordering.

I have a proof of concept patch against the amdvlk Vulkan driver
that allows fp16 rendering and presentation with this format, but
not with the xRGB format. Nicholas already has the test patch in
his inbox. Results look visually correct, also when used on a HDR
monitor.

I also tested with Patch 2/2 on top on a Polaris11 gpu with DCE-11.2
display engine, and also got correct results, so maybe it makes sense
to enable fp16 scanout support also for DCE and not only DCN?
Patch 2/2 does not enable fp16 on DCE 10 or DCE 8, because i don't
have hardware to test it. But it would be nice to expose fp16 on all
supported display engines.

Thanks,
-mario