net: dwc_eth_qos: Set DMA_MODE SWR bit to reset the MAC

net: dwc_eth_qos: Set DMA_MODE SWR bit to reset the MAC

The driver currently only waits for DMA_MODE SWR bit to clear itself.
This is insufficient e.g. on i.MX8M Plus, where the MAC must be reset
before IOMUX GPR[1] content is latched into the MAC and used. Without
the proper reset, the i.MX8M Plus MAC variant does not take the value
in IOMUX GPR[1] into account, which makes it impossible e.g. to switch
interface mode from RGMII to any other.

Since proper reset is desired in general to put the block into defined
state, always assert the DMA_MODE SWR bit before waiting for the bit
to clear itself.

Reviewed-by: Ramon Fried <rfried.dev@gmail.com>
Signed-off-by: Marek Vasut <marex@denx.de>