examples: write the host cdc console over RTT when that is the console

console_write() forwards what the attached CDC device sent back to the
board's console, and reached for board_uart_write() directly to stay
non-blocking. On a board whose console is the debug probe there is no UART:
board_uart_write() is a stub returning -1, so everything the device echoed was
dropped, and the do/while loop retried a write that could never make progress
and spun until more data arrived.

Send it through SEGGER_RTT_Write() on LOGGER_RTT builds -- already
non-blocking in the default NO_BLOCK_SKIP mode, which is what the UART path
wanted board_uart_write() for.

The retry is also bounded now. board_uart_write() is only documented to
return the number of bytes sent, and the stubs disagree on how they say "no
console here" -- lpc40 returns -1, apm32f0xx returns 0 -- so the loop cannot
decide from the return value alone when to stop. It gives up after 10 ms
without progress instead, which no draining console ever hits, and keeps the
negative return as a fast path so a stub UART does not cost that wait on
every read.

The RTT header include lives in board_api.h so any example can reach it; the
include path only exists when LOGGER=rtt defines LOGGER_RTT.

host/cdc_msc_hid now passes on ea4088_quickstart, whose probe (LPC-Link2) has
no VCOM: the CDC echo round-trips through a CH340 with TX-RX shorted.