mesa: automatically detect gallium-xa
What does this MR do and why?
mesa: automatically detect gallium-xa
The "gallium-xa" feature cannot be enabled under certain circumstances, but the meson build detection is unaware of this. As a result, configuring mesa on powerpc64le fails with:
meson.build:663:3: ERROR: Feature gallium-xa cannot be enabled: XA state tracker requires at least one of the following gallium drivers: nouveau, freedreno, i915, svga.
This commit explains to meson.build that if the user has not explicitly enabled gallium-xa, it should be disabled when the above condition is not met.