uhci controller : use new -device syntax

we need an id to allow hotplug

info pci before
---------------
  Bus  0, device   1, function 2:
    USB controller: PCI device 8086:7020
      IRQ 11.
      BAR4: I/O at 0xc040 [0xc05f].
      id ""

info pci after
--------------
  Bus  0, device   1, function 2:
    USB controller: PCI device 8086:7020
      IRQ 11.
      BAR4: I/O at 0xc040 [0xc05f].
      id "uhci"

Signed-off-by: Alexandre Derumier <aderumier@odiso.com>
usb-tablet : always use uhci controller

- usb-tablet on ehci is buggy
- convert to -device syntax

info usb before
----------------
  Device 0.2, Port 1, Speed 12 Mb/s, Product QEMU USB Tablet

info usb after
--------------
  Device 0.2, Port 1, Speed 12 Mb/s, Product QEMU USB Tablet

Signed-off-by: Alexandre Derumier <aderumier@odiso.com>