Input: add vmmouse driver

VMMouse enables low-latency mouse-cursor-movements for VMWare and QEMU
guests.  By removing the guest cursor and using the host as a guest cursor
the cursor movement appears instant although in reality there is some lag.
To be able to do this, the host's view of the cursor position must exactly
match the guest's view and an absolute pointer device is needed. Enter the
VMMouse. While the VMMouse driver has historically been an Xorg user-space
driver, implementing it as a kernel imput driver enables rootless Xorg and
new compositing display servers for VMware guests.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>