kernel - Fix ig4 operation for certain machines

kernel - Fix ig4 operation for certain machines

* Some machine BIOSes use the I2C bus and leave it in a state that causes
  interrupts to not work properly due to a pending interrupt having been
  latched.

* Refactor the code a bit to clear pending interrupts when I2C is enabled.
  This fixes the primary problem.

* Also fix a possible race condition in the interrupt handler where the
  interrupt was being cleared after reading the status instead of before.