Replace a tight busy-wait loop without a pause with a standard
readx_poll_timeout_atomic routine with a 5 us poll period.

Tested by booting a MT7621 device to ensure the driver initializes
properly.

Signed-off-by: Ilya Lipnitskiy <redacted>
---
 drivers/net/ethernet/mediatek/mtk_eth_soc.c | 29 +++++++++------------
 drivers/net/ethernet/mediatek/mtk_eth_soc.h |  2 +-
 2 files changed, 14 insertions(+), 17 deletions(-)

diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
index 8c863322587e..720d73d0c007 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c

@@ -2037,25 +2037,22 @@ static int mtk_set_features(struct net_device *dev, netdev_features_t features)
 /* wait for DMA to finish whatever it is doing before we start using it again */
 static int mtk_dma_busy_wait(struct mtk_eth *eth)
 {
-	unsigned long t_start = jiffies;
+	u32 val;
+	int ret;
+	unsigned int reg;