net: stmmac: dwmac-loongson: Drop pci_enable/disable_msi calls

The Loongson GMAC driver currently doesn't utilize the MSI IRQs, but
retrieves the IRQs specified in the device DT-node. Let's drop the
direct pci_enable_msi()/pci_disable_msi() calls then as redundant

Signed-off-by: Feiyang Chen <chenfeiyang@loongson.cn>
Signed-off-by: Yinggang Gu <guyinggang@loongson.cn>
Reviewed-by: Serge Semin <fancer.lancer@gmail.com>
Acked-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
Tested-by: Serge Semin <fancer.lancer@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>