kconfig/[mn]conf: handle backspace (^H) key

[ Upstream commit 9c38f1f044080392603c497ecca4d7d09876ff99 ]

Backspace is not working on some terminal emulators which do not send the
key code defined by terminfo. Terminals either send '^H' (8) or '^?' (127).
But currently only '^?' is handled. Let's also handle '^H' for those
terminals.

Signed-off-by: Changbin Du <changbin.du@gmail.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Sasha Levin (Microsoft) <sashal@kernel.org>