Update the onenand device to use qemu_log_mask() for reporting
guest errors and unimplemented features, rather than plain
fprintf() and hw_error().

(We leave the hw_error() in onenand_reset(), as that is
triggered by a failure to read the underlying block device
for the bootRAM, not by guest action.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20181115143535.5885-3-peter.maydell@linaro.org