They are defined with the same semantics as the POSIX types,
so prefer those for consistency. Suggested by Peter Maydell.

Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: Aurelien Jarno <aurelien@aurel32.net>
Signed-off-by: NAndreas Färber <andreas.faerber@web.de>
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>