dmaengine: dma: imx-sdma: add fw_loaded and is_ram_script

Add 'fw_loaded' and 'is_ram_script' to check if the script used by channel
is ram script and it's loaded or not, so that could prevent meaningless
following malloc dma descriptor and bd allocate in sdma_transfer_init(),
otherwise memory may be consumed out potentially without free in case
that spi fallback into pio while dma transfer failed by sdma firmware not
ready(next ERR009165 patch depends on sdma RAM scripts/firmware).

Signed-off-by: Robin Gong <yibin.gong@nxp.com>
Acked-by: Vinod Koul <vkoul@kernel.org>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>