linux-user: move TargetFdTrans functions to their own file

This will ease to move out syscall functions from syscall.c

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20180823222215.13781-1-laurent@vivier.eu>
4 files changed