bbconfig: make it independent from printf functions

function                                             old     new   delta
full_write2_str                                        -      25     +25
full_write1_str                                        -      25     +25
clear_main                                            21      20      -1
telnet_main                                         1488    1477     -11
getty_main                                          1932    1918     -14
full_write22_str                                      25       -     -25
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(add/remove: 2/1 grow/shrink: 0/3 up/down: 50/-51)             Total: -1 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
11 files changed