sunxi SOCs can boot from both mmc0 and mmc2, detect from which one we're
booting, and make that one "mmc dev 0" so that a single u-boot binary can
be used for both the onboard eMMC and for external sdcards.
When we're booting from mmc2, we make it dev 0 because that is where the SPL
will load the tertiary payload (the actual u-boot binary in our case) from,
see: common/spl/spl_mmc.c, which has dev 0 hardcoded everywhere.
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk>
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