mmc: core: add helpers mmc_regulator_enable/disable_vqmmc

mmc: core: add helpers mmc_regulator_enable/disable_vqmmc

[ Upstream commit 8d91f3f8ae57e6292142ca89f322e90fa0d6ac02 ]

There's a number of drivers (e.g. dw_mmc, meson-gx, mmci, sunxi) using
the same mechanism and a private flag vqmmc_enabled to deal with
enabling/disabling the vqmmc regulator.

Move this to the core and create new helpers mmc_regulator_enable_vqmmc
and mmc_regulator_disable_vqmmc.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Acked-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Link: https://lore.kernel.org/r/71586432-360f-9b92-17f6-b05a8a971bc2@gmail.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Stable-dep-of: 477865af60b2 ("mmc: sdhci-sprd: Fix vqmmc not shutting down after the card was pulled")
Signed-off-by: Sasha Levin <sashal@kernel.org>