net: stmmac: Use interrupt mode INTM=1 for per channel irq

Enable per DMA channel interrupt that uses shared peripheral
interrupt (SPI), so only per channel TX and RX intr (TI/RI)
are handled by TX/RX ISR without calling common interrupt ISR.

Signed-off-by: Teoh Ji Sheng <ji.sheng.teoh@intel.com>
Signed-off-by: Swee Leong Ching <leong.ching.swee@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>