net/smsc911x: fix irq resource allocation failure

When smsc911x uses GPIO as the interrupt controller, and if both are
loaded as modules, we get following error:

"smsc911x: Could not allocate irq resource"

This issue is because of smsc911x using platform_get_resource to get
device tree based irq resource.

commit "9ec36caf

 (of/irq: do irq resolution in platform_get_irq)" and
commit "7085a7 (drivers: platform: parse IRQ flags from resources)" add
support in platform_get_irq to resolve irq and irq_flags respectively
for both modern device tree and legacy static platform data platforms.

Modify smsc911x driver to use platform_get_irq to pick up irq resource
correctly and use irq_get_trigger_type to get the IRQ trigger flags.

Signed-off-by: Kamlakant Patel <kamlakant.patel@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>