hw/sd: Update trace events for buf+len data

After switching sdbuf and sdcard over to use buf+len instead of single
byte operation, the trace events need to be updated.

This patch updates sdbus_{read,write} and sdcard_write_data to output the
buffer that is worked on.

sdcard_read_data is left unchanged, as it did not print the read byte
before anyways.

Signed-off-by: Christian Speich <c.speich@avm.de>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20260417-sdcard-performance-b4-v4-7-119e66be10c2@avm.de>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>