[ARM] 5606/1: Fix ep93xx watchdog driver headers

Fix a number of build errors in the ep93xx watchdog driver due
to missing io.h

Signed-off-by: Ryan Mallon <ryan@bluewatersys.com>
Acked-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>