keypad boot init overhaul: handle initially held-down keys This change fixes two previous behavioural defects: 1) On Compal phones, the PWR key had to be released before the boot sequence would proceed at all - it was stuck in an endless IRQ loop at the point of Nucleus enabling interrupts, before anything else. 2) On both Compal and sane platforms including Luna, if some regular non-PWR key was held down at boot time, the boot sequence would proceed and complete normally, but all non-PWR keypad buttons would be dead for the remainder of that boot cycle. The fix is a generic solution - no Compal-specific hack ended up being needed for the special case of their idiotic PWON-to-ROW4 hw wiring.