gdb: fix RDEPENDS for PACKAGECONFIG[tui]

gdb: fix RDEPENDS for PACKAGECONFIG[tui]

TUI mode needs terminfo at runtime, which is required to be
explicitly stated in the respective PACKAGECONFIG variable.

Without this change /etc/terminfo/ might be missing, which
leads to a runtime error when trying to use tui, e.g.:
(gdb) tui enable
Cannot enable the TUI: error opening terminal [TERM=xterm-256color]

Signed-off-by: Stefan Tauner <stefan.tauner@artech.at>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>