Initial commit, mostly a import of the minimum from anv/radv to get a
skeleton to start to work with.

In includes:
 * meson files
 * Copy & adapt entrypoints ane extensions scripts from anv (that were
   later used on radv)

This is a firt approach, but is is likely that we can remove/simplify
some things.

v2: fix copyright character at broadcom/vulkan/meson.build (Eric)
v3: no spaces inside arrays (Dylan)
v4: add gnu_symbol_visibility (detected by CI on first Merge attemp)

Reviewed-by: Eric Anholt <eric@anholt.net>

squash! v3dv: add v3d vulkan driver skeleton

Part-of: <!6766>