net: stmmac: Fix PHY interrupt enable

Set the phy irq from POLL to INTR mode and make sure
the register are set correctly.

Change-Id: I8ed06b0029920fcd003b008b188bdbe00467a03d
Acked-by: Abhishek Chauhan <abchauha@qti.qualcomm.com>
Signed-off-by: Sunil Paidimarri <hisunil@codeaurora.org>