[ARM] 4553/1: ARM at91: define FIQ_START

For ARM at91, the FIQ_START #define is required if you use a driver
that enables FIQ support.

Signed-off-by: Karl Olsen <karl@micro-technic.com>
Acked-by: Andrew Victor <andrew at sanpeople.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>