Modifying a generic header like watchdog.h, removing not directly used
asm/ptrace.h header relies on whoever includes it to already have
included something that defines the type ulong.

Make the asm/ptrace.h header self-contained by including the proper
header.

Signed-off-by: Rasmus Villemoes <ravi@prevas.dk>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Stefan Roese <sr@denx.de>