Added _stdio_close.c and __stdio_seek.c from musl
First commit musl_system.c/h - system implementation for musl

Since microcontroller don't have a syscall like linux, the musl_system.h
header file defines functions that musl calls back to the microcontroller
code.  These are the syscall functions.  In this commit two functions
have been added-

system_close - low level close FILE
system_seek - low level seek FILE
Added __stdout_write.c from musl library
Added system_stdout_write() function

This function should write out the supplied buffer to the stdout
device - ie. uart port, usb port, etc.
Added dfu.py from micropython