dma-buf: heaps: system: Turn the heap into a module

dma-buf: heaps: system: Turn the heap into a module

The system heap can be easily turned into a module by adding the usual
MODULE_* macros, importing the proper namespaces and changing the
Kconfig symbol to a tristate.

This heap won't be able to unload though, since we're missing a lot of
infrastructure to make it safe.

Reviewed-by: T.J. Mercier <tjmercier@google.com>
Acked-by: Andrew Davis <afd@ti.com>
Signed-off-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
Link: https://patch.msgid.link/20260427-dma-buf-heaps-as-modules-v5-3-b6f5678feefc@kernel.org