drivers: dm8806: link speed change interrupt handling

On the interrupt handling, one thread per driver instance is involved
into monitoring the semaphor, sends inside the gpio callback triggered
by the gpio interrupt. Each time, when the link parameters are change,
the DM8806 is generating the gpio interrupt. After getting semaphor,
the application callback function which was linked during initialization
process is called to get the new link parameters with standard API
calls

Signed-off-by: Robert Slawinski <robert.slawinski1@gmail.com>