[ARM] 3871/1: S3C24XX: Fix ordering of EINT4..23

The demux code for the IRQ EINTs above 3 was
using find last set instead of finding first
set.

Also fix it so that we only check EINT4..7
when the parent EINT4t7 goes off, and the
8..23 when EINT8t23 goes off.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>