etnaviv: pass a preallocated variant to compiler

etnaviv: pass a preallocated variant to compiler

In the long run the compiler needs to know the specifc variant
'key' in order to compile appropriate assembly. With this commit
the variant knows its shader and we are able pass the preallocated
variant into etna_compile_shader(..). This saves us from passing
extra ptrs everywhere.

Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>