Enable HAVE_DMA_CONTIGUOUS, reserve contiguous memory at bootmem_init, use dma_alloc_from_contiguous and dma_release_from_contiguous in xtensa_dma_alloc/free. This allows for big contiguous DMA buffer allocation from designated area configured in the device tree. Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>