mmc: sdhci: Balance vmmc regulator_enable(), and always enable vqmmc

The vmmc regulator enable in sdhci_add_host is NOT necessary since
it can be enabled during mmc_power_up by function mmc_regulator_set_ocr.
And this extra enable will make regulator_enable/regulator_disable
unbalanced. Consequently, vmmc can't be disabled during mmc_power_off.

Also, if the vqmmc regulator exists, it should be enabled regardless it
support 1.8v or not.

Signed-off-by: Kevin Liu <kliu5@marvell.com>
Signed-off-by: Philip Rakity <prakity@marvell.com>
Signed-off-by: Chris Ball <cjb@laptop.org>