Add a driver for PS/2 keyboards

[maxmitchelson]

Setup the PS/2 controller appropriately and create a driver for handling keyboard scan codes. Link the whole thing with the shell.

Resources

• Relevant OS dev wiki articles: ISO8042 Controller, PS/2, PS/2 Keyboards
• Timer sources on x86-64 if needed: Timers, IOAPIC (Hardware PIC interrupts), HPET