mesa: Replace dri-native with dri for native and nativesdk classes
Instead of using a native specific packageconfig option, we now set
the swrast as the supported driver.
Currently the native version does not build any dri drivers at all.
This is intentional: mesa-native is used only by virgl, so was made
the most minimal possible configuration for mesa-native so that a)
virgl works; and b) build time is as short as possible.
There are two swrast drivers, one dri-based, another gallium-based.
Autotools lets you build both, meson forces you to choose.
Thus DRIDRIVERS = "swrast" is only set for _native, as for _target
we get the gallium driver instead.
See discussion here [1]
Based on https://patchwork.openembedded.org/patch/158748/
