net: stmmac: dwc-qos: clean up clock initialisation

Clean up the clock initialisation by providing a helper to find a
named clock in the bulk clocks, and provide the name of the stmmac
clock in match data so we can locate the stmmac clock in generic
code.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Tested-by: Thierry Reding <treding@nvidia.com>
Link: https://patch.msgid.link/E1tmbhj-004vSz-Pt@rmk-PC.armlinux.org.uk


Signed-off-by: Jakub Kicinski <kuba@kernel.org>