[EMULATORS] Introduce PS/2 emulator and PL050 emulator

This patch introduces PS/2 based input device emulators.

It precisely adds following stuff:
1. PS/2 device emulation APIs
2. PL050 (or AMBA KMI) keyboard/mouse interface emulator

All input device emulators will have to use newly introduced
vmm_vinput framework to provide virtual input devices to Xvisor.

Signed-off-by: Anup Patel <anup@brainfault.org>