ARM: 6414/1: ux500: DB5500 generic modem IRQ handler

This is a (threaded) IRQ handler for the modems that appear from the
modem part of the DB5500 ASIC.

Signed-off-by: Stefan Nilsson XK <stefan.xk.nilsson@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>