stmmac: intel: Convert to use pci_alloc_irq_vectors() API

pci_enable_msi() is deprecated API, thus, switch to modern
pci_alloc_irq_vectors().

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>