Add XipCs1 function

[thejpster]

It's FUNCSEL 9

[jonathanpallant]

OK, so the problem is the FuncSel value of 9 does different things depending on the pin. But we've flattened it into one enum to cover all the pins.

I guess we could call number 9 CS1_CLOCK_TRACE?

[jannic]

There's already an entry for funcsel 9 in the PAC:

      #[doc = "9: Connect to GPCK peripheral"]
      GPCK = 9,

We can't have multiple variants with the same numeric value, so all we could do is rename this variant.

[jonathanpallant]

Yup

[thejpster]

So I think we just leave this and fix it in the HAL