v3d: add support for on-disk shader cache

v3d: add support for on-disk shader cache

It stores the compiled shaders on disk so further executions will load
them from disk instead of compiling, improving the overall performance.

This is noticeable in games where they suddenly get stuck for a while
because they start to compile one or more shaders.

v2:
 - Remove comment (Alejandro)
 - Use malloc() + helper to simplify code (Alejandro)

Signed-off-by: Juan A. Suarez Romero <jasuarez@igalia.com>
Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15380>