drm/vmwgfx: Replace vmw_dma_buffer with vmw_buffer_object

Initially vmware buffer objects were only used as DMA buffers, so the name
DMA buffer was a natural one. However, currently they are used also as
dumb buffers and MOBs backing guest backed objects so renaming them to
buffer objects is logical. Particularly since there is a dmabuf subsystem
in the kernel where a dma buffer means something completely different.

This also renames user-space api structures and IOCTL names
correspondingly, but the old names remain defined for now and the ABI
hasn't changed.

There are a couple of minor style changes to make checkpatch happy.

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