xen: cleanup unrealized flash devices

xen: cleanup unrealized flash devices

The generic pc_machine_initfn() calls pc_system_flash_create() which creates
'system.flash0' and 'system.flash1' devices. These devices are then realized
by pc_system_flash_map() which is called from pc_system_firmware_init() which
itself is called via pc_memory_init(). The latter however is not called when
xen_enable() is true and hence the following assertion fails:

qemu-system-i386: hw/core/qdev.c:439: qdev_assert_realized_properly:
Assertion `dev->realized' failed

These flash devices are unneeded when using Xen so this patch avoids the
assertion by simply removing them using pc_system_flash_cleanup_unused().

Reported-by: Jason Andryuk <jandryuk@gmail.com>
Fixes: ebc29e1beab0 ("pc: Support firmware configuration with -blockdev")
Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Tested-by: Jason Andryuk <jandryuk@gmail.com>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200624121841.17971-3-paul@xen.org>
Fixes: dfe8c79c4468 ("qdev: Assert onboard devices all get realized properly")
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>