blitter: cache blit programs in a hash table

Instead of just caching the fragment shaders and use some tables
cache all shaders and use a hash table.

Related: https://gitlab.freedesktop.org/virgl/virglrenderer/-/issues/125

Signed-off-by: Gert Wollny <gert.wollny@collabora.com>
Reviewed-by: Corentin Noël <corentin.noel@collabora.com>.