tools: kwboot: Add support for backspace key in mini terminal

Marvell BootROM recognize only '\b' byte as backspace. Use terminfo
for retrieving current backspace sequence and replace any occurrence of
backspace sequence by the '\b' byte.

Reading terminfo database is possible via tigetstr() function from system
library libtinfo.so.*. So link kwboot with -ltinfo.

Normally terminfo functions are in <term.h> system header file. But this
header file conflicts with U-Boot "termios_linux.h" header file. So declare
terminfo functions manually.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Stefan Roese <sr@denx.de>
Tested-by: Stefan Roese <sr@denx.de>