net: stmmac: Make MSI interrupt routine generic

There is no support for per DMA channel interrupt for non-MSI platform,
where the MAC's per channel interrupt hooks up to interrupt controller(GIC)
through shared peripheral interrupt(SPI) to handle interrupt from TX/RX
transmit channel.

This patch generalize the existing MSI ISR to also support non-MSI
platform.

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>