arm64/imx9: Allocate 64B granules instead of 256B

Optimal size of granule is 64B (the dcache line size).
We can use it now as we don't have max. 32 granules limitation anymore.

Signed-off-by: Jani Paalijarvi <jani.paalijarvi@unikie.com>

arch/arm64/src/imx9/imx9_dma_alloc.c

@@ -89,11 +89,7 @@ int imx9_dma_alloc_init(void)
 {
   /* Allocate 64B granules with 64B alignment */
 
-  /* REVISIT: Use 256B granule size to get 8K maximum allocation. This is a
+  dma_allocator = gran_initialize(g_dma_heap, sizeof(g_dma_heap), 6, 6);
-   * limitation in the granule allocator itself.
-   */
-
-  dma_allocator = gran_initialize(g_dma_heap, sizeof(g_dma_heap), 8, 6);
 
   if (dma_allocator == NULL)
     {