net: mediatek: stop using bitfileds for DMA descriptors

net: mediatek: stop using bitfileds for DMA descriptors

This patch is a preparation for adding a new version of PDMA of which the
DMA descriptor fields has changed. Using bitfields will result in a complex
modification. Convert bitfields to u32 units can solve this problem easily.

Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Daniel Golle <daniel@makrotopia.org>
Signed-off-by: Weijie Gao <weijie.gao@mediatek.com>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>