net: ethernet: ti: add missing GENERIC_ALLOCATOR dependency

This patch mades TI_DAVINCI_CPDMA select GENERIC_ALLOCATOR.
without that, the following sparc64 build failure happen

drivers/net/ethernet/ti/davinci_cpdma.o: In function `cpdma_check_free_tx_desc':
(.text+0x278): undefined reference to `gen_pool_avail'
drivers/net/ethernet/ti/davinci_cpdma.o: In function `cpdma_chan_submit':
(.text+0x340): undefined reference to `gen_pool_alloc'
(.text+0x5c4): undefined reference to `gen_pool_free'
drivers/net/ethernet/ti/davinci_cpdma.o: In function `__cpdma_chan_free':
davinci_cpdma.c:(.text+0x64c): undefined reference to `gen_pool_free'
drivers/net/ethernet/ti/davinci_cpdma.o: In function `cpdma_desc_pool_destroy.isra.6':
davinci_cpdma.c:(.text+0x17ac): undefined reference to `gen_pool_size'
davinci_cpdma.c:(.text+0x17b8): undefined reference to `gen_pool_avail'
davinci_cpdma.c:(.text+0x1824): undefined reference to `gen_pool_size'
davinci_cpdma.c:(.text+0x1830): undefined reference to `gen_pool_avail'
drivers/net/ethernet/ti/davinci_cpdma.o: In function `cpdma_ctlr_create':
(.text+0x19f8): undefined reference to `devm_gen_pool_create'
(.text+0x1a90): undefined reference to `gen_pool_add_virt'
Makefile:1011: recipe for target 'vmlinux' failed

Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: David S. Miller <davem@davemloft.net>