Removing splxxx functions

I intend to remove all the splxxx functions.

Firewire, syscons, smbfs and tpm are the only things that use them.

I plan on copying the function definitions to relevant header files... Or
just deleting the function calls since they've been a nop now just shy of
two decades (depending on how you count things).

I'll leave it to others to decide if any of these should be deprecated in a
separate thread.

Comments?

Warner