mmc: sdio: Extend sdio_config_attr macro and use it also for modalias

This simplify code for generating sdio config attributes and allows easily
define new sdio attributes.

Signed-off-by: Pali Rohár <pali@kernel.org>
Link: https://lore.kernel.org/r/20200727133837.19086-4-pali@kernel.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>