Some devices do not make use of the CMD0/DAT0/DAT2 direction control
pins of the MMC/SD card 0 interface. In this case we should leave
those pins unconfigured.

A similar case already exists for "mc1_a_1" vs "mc1_a_2"
when the MC1_FBCLK pin is not used.

Add a new "mc0_a_2" pin group which is equal to "mc0_a_1" except
with the MC0_CMDDIR, MC0_DAT0DIR and MC0_DAT2DIR pins removed.
Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Link: https://lore.kernel.org/r/20191117205439.239211-1-stephan@gerhold.netSigned-off-by: Linus Walleij <linus.walleij@linaro.org>