net: ethernet: ti: davinci_cpdma: add missing EXPORTs

As of commit 8f32b909
("net: ethernet: ti: davinci_cpdma: add set rate for a channel") the
ARM allmodconfig builds would fail modpost with:

ERROR: "cpdma_chan_set_weight" [drivers/net/ethernet/ti/ti_cpsw.ko] undefined!
ERROR: "cpdma_chan_get_rate" [drivers/net/ethernet/ti/ti_cpsw.ko] undefined!
ERROR: "cpdma_chan_get_min_rate" [drivers/net/ethernet/ti/ti_cpsw.ko] undefined!
ERROR: "cpdma_chan_set_rate" [drivers/net/ethernet/ti/ti_cpsw.ko] undefined!

Since these weren't declared as static, it is assumed they were
meant to be shared outside the file, and that modular build testing
was simply overlooked.

Fixes: 8f32b909 ("net: ethernet: ti: davinci_cpdma: add set rate for a channel")
Cc: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>
Cc: Mugunthan V N <mugunthanvnm@ti.com>
Cc: Grygorii Strashko <grygorii.strashko@ti.com>
Cc: linux-omap@vger.kernel.org
Cc: netdev@vger.kernel.org
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>