can: mcp251x: Allow pass IRQ flags through platform data.

When an interrupt occurs, the INT pin is driven low by the
MCP251x controller (falling edge) but in some cases the INT
pin can be connected to the MPU through a transistor or level
translator which inverts this signal. In this case interrupt
should be configured in rising edge.

This patch adds support to pass the IRQ flags via
mcp251x_platform_data.

Signed-off-by: Enric Balletbo i Serra <eballetbo@iseebcn.com>
Acked-by: Wolfgang Grandegger <wg@grandegger.com>
Acked-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>