REGMAP_MMIO is not user-configurable, so we can only satisfy this
dependency by enabling some other Kconfig symbol that properly 'select's
it. Use select like everybody else.

Noticed when trying to enable this driver for compile testing.

Fixes: 59592cc1 ("mmc: sdhci_am654: Add dependency on MMC_SDHCI_AM654")
Signed-off-by: Brian Norris <briannorris@chromium.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20221024180300.2292208-1-briannorris@chromium.orgSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>