linux-user: move arm/aarch64/m68k fcntl definitions to [arm|aarch64|m68k]/target_fcntl.h

No code change.

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Acked-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20180529194207.31503-5-laurent@vivier.eu>