The WM9712 can be configured by resistor strapping GPIO4 to behave like
the WM9713 and default to leaving the AC97 link disabled after cold
reset until a warm reset occurs.  In this configuration we need to issue
a warm reset after cold to bring the link up so do so.  The warm reset
will be harmless on systems that don't need it.

[Changelog rewritten to document the reasoning. -- broonie]

Signed-off-by: Marek Vasut <marek.vasut@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>