mmc: sdhci: Request regulators before reading capabilities

The capabilities of the SDHCI host controller are read early during the
SDHCI host initialisation in sdhci_setup_host() and before any
regulators for the host have been requested. This means that if the host
supports some high-speed modes (according to its capabilities register),
but the board cannot because the appropriate voltage regulator is not
available, then the host cannot easily override the capabilities that
are supported.

To allow a SDHCI host controller to determine if it can support UHS high
speed modes via the presence of the MMC regulators, request the
regulators before reading the capabilities of the host controller. This
will allow the SDHCI host to use the 'reset' callback to take the
appropriate action (set flags, configure registers, etc) before the
capabilities register(s) are read.

Please note that some SDHCI hosts, such as the Tegra SDHCI host, has
the ability to mask bits in the capabilities register to prevent
certain capabilities from being advertised.

Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

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