iosys-map: Add IOSYS_MAP_INIT_VADDR_IOMEM()

Add IOSYS_MAP_INIT_VADDR_IOMEM() for static init of variables of type
struct iosys_map.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220808125406.20752-2-tzimmermann@suse.de