panfrost: Unify bifrost_scratchpad with mali_shared_memory

It looks like these are the same structure, so this allows us to reuse
mali_shared_memory across architectures, and dispels with the
Bifrost-specific mystery of the scratchpads... nothing so mysterious
after all, just stack.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3835>
4 files changed