drivers: net: cpsw: make cpsw_ale.c a module to allow re-use on Keystone

NetCP on Keystone has cpsw ale function similar to other TI SoCs
and this driver is re-used. To allow both ti cpsw and keystone netcp
to re-use the driver, convert the cpsw ale to a module and configure
it through Kconfig option CONFIG_TI_CPSW_ALE. Currently it is statically
linked to both TI CPSW and NetCP and this causes issues when the above
drivers are built as dynamic modules. This patch addresses this issue

While at it, fix the Makefile and code to build both netcp_core and
netcp_ethss as dynamic modules. This is needed to support arm allmodconfig.
This also requires exporting of API calls provided by netcp_core so that
both the above can be dynamic modules.

Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Acked-by: Mugunthan V N <mugunthanvnm@ti.com>
Tested-by: Mugunthan V N <mugunthanvnm@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>