mmc: host: Drop redundant MMC_CAP_ERASE

The MMC_CAP_ERASE bit is no longer used by the mmc core as erase, discard
and trim operations are now always supported. Therefore, drop the bit and
move all mmc hosts away from using it.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Rui Miguel Silva <rmfrfs@gmail.com>
Link: https://lore.kernel.org/r/20200508112902.23575-1-ulf.hansson@linaro.org
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>