RDMA/uverbs: select CONFIG_DMA_SHARED_BUFFER

The addition of dmabuf support in uverbs means that it is no
longer possible to build infiniband support if that is disabled:

arm-linux-gnueabi-ld: drivers/infiniband/core/ib_core_uverbs.o: in function `rdma_user_mmap_entry_remove.part.0':
ib_core_uverbs.c:(.text+0x508): undefined reference to `dma_buf_move_notify'
(dma_buf_move_notify): Unknown destination type (ARM/Thumb) in drivers/infiniband/core/ib_core_uverbs.o
ib_core_uverbs.c:(.text+0x518): undefined reference to `dma_resv_wait_timeout'
(dma_resv_wait_timeout): Unknown destination type (ARM/Thumb) in drivers/infiniband/core/ib_core_uverbs.o

Select this from Kconfig, as we do for the other users.

Fixes: 0ac6f4056c4a ("RDMA/uverbs: Add DMABUF object type and operations")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://patch.msgid.link/20260216121213.2088910-1-arnd@kernel.org
Signed-off-by: Leon Romanovsky <leon@kernel.org>