hw/riscv: microchip_pfsoc: Connect a Cadence SDHCI controller and an SD card

Microchip PolarFire SoC integrates one Cadence SDHCI controller.
On the Icicle Kit board, one eMMC chip and an external SD card
connect to this controller depending on different configuration.

As QEMU does not support eMMC yet, we just emulate the SD card
configuration. To test this, the Hart Software Services (HSS)
should choose the SD card configuration:

$ cp boards/icicle-kit-es/def_config.sdcard .config
$ make BOARD=icicle-kit-es

The SD card image can be built from the Yocto BSP at:
https://github.com/polarfire-soc/meta-polarfire-soc-yocto-bsp



Note the generated SD card image should be resized before use:
$ qemu-img resize /path/to/sdcard.img 4G

Launch QEMU with the following command:
$ qemu-system-riscv64 -nographic -M microchip-icicle-kit -sd sdcard.img

Signed-off-by: Bin Meng <bin.meng@windriver.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <1598924352-89526-9-git-send-email-bmeng.cn@gmail.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>