drm/etnaviv: Drop local dma_parms

Since commit 9495b7e9

 ("driver core: platform: Initialize dma_parms
for platform devices"), struct platform_device already provides a
dma_parms structure, so we can save allocating another one.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>