net: stmmac: dwmac_lib: enlarge dma reset timeout

If the phy enables power saving technology, the dwmac's software reset
needs more time to complete, enlarge dma reset timeout to 200000us.

Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Link: https://lore.kernel.org/r/20201113090902.5c7aab1a@xhacker.debian
Signed-off-by: Jakub Kicinski <kuba@kernel.org>