aspeed/smc: Only wire flash devices at reset

The Aspeed machines have many Static Memory Controllers (SMC), up to
8, which can only drive flash memory devices. Commit 27a2c66c92
("aspeed/smc: Wire CS lines at reset") tried to ease the definitions
of these devices by allowing flash devices from the command line to be
attached to a SSI bus. For that, the wiring of the CS lines of the
Aspeed SMC controller was moved at reset. Two assumptions are made
though, first that the device has a SSI_GPIO_CS GPIO line, which is
not always the case, and second that it is a flash device.

Correct this problem by ensuring that the devices attached to the bus
are of the correct flash type. This fixes a QEMU abort when devices
without a CS line, such as the max111x, are passed on the command
line.

While at it, export TYPE_M25P80 used in the Xilinx Versal Virtual
machine.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2228
Fixes: 27a2c66c92 ("aspeed/smc: Wire CS lines at reset")
Reported-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Tested-by: Thomas Huth <thuth@redhat.com>
[ clg: minor fixes in the commit log ]
Signed-off-by: Cédric Le Goater <clg@redhat.com>

include/hw/block/flash.h

@@ -78,6 +78,8 @@ extern const VMStateDescription vmstate_ecc_state;
 
 /* m25p80.c */
 
+#define TYPE_M25P80 "m25p80-generic"
+
 BlockBackend *m25p80_get_blk(DeviceState *dev);
 
 #endif