e1000e: default IntMode based on kernel config & available hardware support

Based on a patch from Prabhakar Kushwaha <prabhakar@freescale.com>, set
appropriate default interrupt mode dependent on whether CONFIG_PCI_MSI
is enabled in the kernel configuration and if the hardware supports
MSI-X.  Set the module parameter log message accordingly.

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Cc: Jin Qing <b24347@freescale.com>
Cc: Prabhakar Kushwaha <prabhakar@freescale.com>
Cc: Jin Qing <b24347@freescale.com>
Cc: Kumar Gala <galak@kernel.crashing.org>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>