ARM: mxc: Remove test_for_ltirq

The patch "ARM: gic: consolidate PPI handling" removes the usage
of test_for_ltirq. After the merge of imx6q remove this there, too.

Cc: Sascha Hauer <kernel@pengutronix.de>
Signed-off-by: Dirk Behme <dirk.behme@de.bosch.com>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>