hw/sd/sdhci: Document the datasheet used

Add datasheet name in the file header.

We can not add the direct download link since there is a disclaimers
to agree first on the SD Association website (www.sdcard.org).

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Tested-by: Alexander Bulekov <alxndr@bu.edu>
Message-Id: <20200901140411.112150-3-f4bug@amsat.org>
1 file changed