drm/vmwgfx: Add a kernel interface to create a framebuffer v2

The kernel interface is needed for fbdev, and needs to be free from
a file_priv member. To accomplish this, remove the fb surface mutex
and list which isn't used anymore, anyway.

Finally, make the pin() and unpin() pin the framebuffer for all display
system backends, so that fbdev can pin its framebuffer before mapping it.

v2: Address review comments:
- Fix vmw_framebuffer_unpin() to handle also the surface framebuffer case.
- Fix vmw_kms_new_framebuffer() to actually use the only_2d parameter.

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