kernel - Implement CHECKTIMEOUT() abstraction

kernel - Implement CHECKTIMEOUT() abstraction

* Implement a CHECKTIMEOUT() abstraction which allows us to remove retry
  counts from low level device driver loops and replace them with a
  timeout polling routine.

* Use in the keyboard code so we no longer make assumptions on how long
  it takes to inb/outb the keyboard controller.  Some BIOSes do not have
  a keyboard controller at all and emulate the ports via SMI, which is
  much much slower than accessing a real port.