freedreno-dummy: It is wiser to allocate a BO before mapping it

Signed-off-by: Tomasz Figa <tomasz.figa@gmail.com>
xf86drm_dummy: Implement fake auth support

Signed-off-by: Tomasz Figa <tomasz.figa@gmail.com>
xf86drm_dummy: Stub few more mode setting IOCTLs

Signed-off-by: Tomasz Figa <tomasz.figa@gmail.com>
xf86drm_dummy: Return /dev/null as card device name

This makes it possible to at least open it. A workaround for code that
opens DRM device directly instead of calling drmOpen*.

Signed-off-by: Tomasz Figa <tomasz.figa@gmail.com>