All the SHDIs can operate with either 3.3V or 1.8V signals, depending
on negotiation with the card.

Based on work by Wolfram Sang for the r8a7790.
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Acked-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>