linux-user/arm: Move target_oabi_flock64 out of target_structs.h

linux-user/arm: Move target_oabi_flock64 out of target_structs.h

Place it next to copy_from/to_user_oabi_flock64, the only users,
inside the existing target-specific ifdef.  This leaves only
generic ipc structs in target_structs.h.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20220107042600.149852-2-richard.henderson@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>