BACKPORT: UPSTREAM: net: stmmac: Use mutex instead of spinlock

Some drivers, such as DWC EQOS on Tegra, need to perform operations that
can sleep under this lock (clk_set_rate() in tegra_eqos_fix_speed()) for
proper operation. Since there is no need for this lock to be a spinlock,
convert it to a mutex instead.

Fixes: e6ea2d16 ("net: stmmac: dwc-qos: Add Tegra186 support")
Reported-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Tested-by: Bhadram Varka <vbhadram@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 29555fa3
https://github.com/torvalds/linux.git

)
Signed-off-by: Vinod Koul <vkoul@kernel.org>