mmc: renesas_sdhi: handle M3-W ES1.2 and 1.3 revisions

For ES1.2, add a comment explaining the situation. For ES1.3 (and
later, although unlikely), add a new entry defining it as 4tap.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/20200423130432.9990-2-wsa+renesas@sang-engineering.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>