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 <[email protected]>
Acked-by: Andrew Davis <[email protected]>
Signed-off-by: Maxime Ripard <[email protected]>
Signed-off-by: Sumit Semwal <[email protected]>
Link: https://patch.msgid.link/[email protected]

drivers/dma-buf/heaps/Kconfig

@@ -1,5 +1,5 @@
 config DMABUF_HEAPS_SYSTEM
-	bool "DMA-BUF System Heap"
+	tristate "DMA-BUF System Heap"
 	depends on DMABUF_HEAPS
 	help
 	  Choose this option to enable the system dmabuf heap. The system heap

drivers/dma-buf/heaps/system_heap.c

@@ -537,3 +537,8 @@ static int __init system_heap_create(void)
 	return 0;
 }
 module_init(system_heap_create);
+
+MODULE_DESCRIPTION("DMA-BUF System Heap");
+MODULE_LICENSE("GPL");
+MODULE_IMPORT_NS("DMA_BUF");
+MODULE_IMPORT_NS("DMA_BUF_HEAP");