drm/vmwgfx: Add VMWare host messaging capability

This patch adds capabilities for a VMWare guest to send and
receive messages from the host, and adds functions to sending log
messages to vmware.log and to request device settings that aren't
available through the virtual hardware, e.g. certain settings in
the VMX file.

Signed-off-by: Sinclair Yeh <syeh@vmware.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>