mmc: sdhci_am654: Add dependency on MMC_SDHCI_AM654

Fix build error:

drivers/mmc/host/sdhci_am654.o: In function `sdhci_am654_probe':
drivers/mmc/host/sdhci_am654.c:464: undefined reference to `__devm_regmap_init_mmio_clk'
drivers/mmc/host/sdhci_am654.o:(.debug_addr+0x3f8): undefined reference to `__devm_regmap_init_mmio_clk'

Reported-by: Hulk Robot <hulkci@huawei.com>
Fixes: aff88ff23512 ("mmc: sdhci_am654: Add Initial Support for AM654 SDHCI driver")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>