shell: uart: Fix wait for DTR before TX

Fail compilation when incorrect configuration is detected, i.e. when
SHELL_BACKEND_SERIAL_CHECK_DTR is set but UART_LINE_CTRL is not set.

Use periodic timer to wait for DTR instead of waiting in uart callback
to prevent blocking caller workqueue and/or sleeping in ISR.

DTR check was only ever supported with interrupt driven backend so add
appropriate depends on to Kconfig.

Fixes: e9f23888 ("shell: uart: Add waiting on DTR signal before
sending data")
Fixes: #47120
Fixes: #54705

Signed-off-by: Tomasz Moń <tomasz.mon@nordicsemi.no>