mmc: sdhci-of-at91: set clocks and presets after resume from deepest PM

This adds deepest (Backup+Self-Refresh) PM support to the ATMEL SAMA5D2
SoC's SDHCI controller.

When resuming from deepest state, it is required to restore preset
registers as the registers are lost since VDD core has been shut down
when entering deepest state on the SAMA5D2. The clocks need to be
reconfigured as well.

The other registers and init process are taken care of by the SDHCI
core.

Signed-off-by: Quentin Schulz <quentin.schulz@free-electrons.com>
Acked-by: Ludovic Desroches <ludovic.desroches@microchip.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>