test/py: mmc: Add 'mmc info' test

Add test for 'mmc info' subcommand. This tests whether the card
information is obtained correctly and verifies the device, bus
speed, bus mode and bus width.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Tom Rini <trini@konsulko.com>
Cc: Simon Glass <sjg@chromium.org>
Reviewed-by: Simon Glass <sjg@chromium.org>