hw/ppc/e500: Add Freescale eSDHC to e500plat

Adds missing functionality to e500plat machine which increases the
chance of given "real" firmware images to access SD cards.

Signed-off-by: Bernhard Beschow <shentey@gmail.com>
Message-Id: <20221018210146.193159-8-shentey@gmail.com>
[PMD: Simplify using create_unimplemented_device("esdhc")]
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Bernhard Beschow <shentey@gmail.com>
Reviewed-by: Bernhard Beschow <shentey@gmail.com>
Message-Id: <20221101222934.52444-4-philmd@linaro.org>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>

docs/system/ppc/ppce500.rst

@@ -19,6 +19,7 @@ The ``ppce500`` machine supports the following devices:
 * Power-off functionality via one GPIO pin
 * 1 Freescale MPC8xxx PCI host controller
 * VirtIO devices via PCI bus
+* 1 Freescale Enhanced Secure Digital Host controller (eSDHC)
 * 1 Freescale Enhanced Triple Speed Ethernet controller (eTSEC)
 
 Hardware configuration information
@@ -180,3 +181,15 @@ as follows:
       -kernel vmlinux \
       -drive if=pflash,file=/path/to/rootfs.ext2,format=raw \
       -append "rootwait root=/dev/mtdblock0"
+
+Alternatively, the root file system can also reside on an emulated SD card
+whose size must again be a power of two:
+
+.. code-block:: bash
+
+  $ qemu-system-ppc64 -M ppce500 -cpu e500mc -smp 4 -m 2G \
+      -display none -serial stdio \
+      -kernel vmlinux \
+      -device sd-card,drive=mydrive \
+      -drive id=mydrive,if=none,file=/path/to/rootfs.ext2,format=raw \
+      -append "rootwait root=/dev/mmcblk0"