hw/sd: Add sdbus_read_data() to read multiples bytes on the data line

hw/sd: Add sdbus_read_data() to read multiples bytes on the data line

Add a sdbus_read_data() method to read multiple bytes on the
data line of a SD bus.
We might improve the tracing later, for now keep logging each
byte individually.

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20200814092346.21825-7-f4bug@amsat.org>