drivers/virt: introduce Freescale hypervisor management driver

Add the drivers/virt directory, which houses drivers that support
virtualization environments, and add the Freescale hypervisor management
driver.

The Freescale hypervisor management driver provides several services to
drivers and applications related to the Freescale hypervisor:

1. An ioctl interface for querying and managing partitions

2. A file interface to reading incoming doorbells

3. An interrupt handler for shutting down the partition upon receiving the
   shutdown doorbell from a manager partition

4. A kernel interface for receiving callbacks when a managed partition
   shuts down.

Signed-off-by: Timur Tabi <timur@freescale.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>