TI Davinci EMAC : add platform specific interrupt enable/disable logic.

On certain SOCs, the EMAC controller is interfaced with a wrapper logic
for handling interrupts. This  patch implements a platform
specific hook to cater to platforms that require custom interrupt
handling logic

Signed-off-by: Sriramakrishnan <srk@ti.com>
Acked-by: Chaithrika U S <chaithrika@ti.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>