Since we can now send packets of arbitrary length:
simplify gdb_monitor_write() and send the whole payload
in one packet.

Suggested-by: Luc Michel <luc.michel@greensocs.com>
Signed-off-by: Damien Hedde <damien.hedde@greensocs.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20191211160514.58373-3-damien.hedde@greensocs.com>
Message-Id: <20200316172155.971-28-alex.bennee@linaro.org>