TI: plugin_store: rename C2DmaBufAllocator -> C2CustomHeapDmaBufAllocator

Since this is version of C2DmaBufAllocator will use a different
dmabuf heap, rename it to C2CarveoutDmaBufAllocator to reflect a
different usage.

Having a different name will be helpful when skimming through logcat.

Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Signed-off-by: Guillaume La Roque <glaroque@baylibre.com>