hw/arm/exynos: Add generic SDHCI devices

hw/arm/exynos: Add generic SDHCI devices

Exynos4210 has four SD/MMC controllers supporting:
 - SD Standard Host Specification Version 2.0,
 - MMC Specification Version 4.3,
 - SDIO Card Specification Version 2.0,
 - DMA and ADMA.

Add emulation of SDHCI devices which allows accessing storage through SD
cards. Differences from real hardware:
 - Devices are shipped with eMMC memory, not SD card.
 - The Exynos4210 SDHCI has few more registers, e.g. for
   controlling the clocks, additional status (0x80, 0x84, 0x8c). These
   are not implemented.

Testing on smdkc210 machine with "-drive file=FILE,if=sd,bus=0,index=2".

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Message-id: 20170422190709.8676-1-krzk@kernel.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>