net: ipa: have gsi_irq_setup() return an error code

Change gsi_irq_setup() so it returns an error value, and introduce
gsi_irq_teardown() as its inverse.  Set the interrupt type (IRQ
rather than MSI) in gsi_irq_setup().

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>