fbdev: wm8505fb: select CONFIG_FB_IOMEM_FOPS

The fb_io_mmap() function is used in the file operations but
not enabled in all configurations unless FB_IOMEM_FOPS gets
selected:

ld.lld-20: error: undefined symbol: fb_io_mmap
referenced by wm8505fb.c
drivers/video/fbdev/wm8505fb.o:(wm8505fb_ops) in archive vmlinux.a

Fixes: 11754a504608 ("fbdev/wm8505fb: Initialize fb_ops to fbdev I/O-memory helpers")
Signed-off-by: Arnd Bergmann <[e-mail]>
Reviewed-by: Thomas Zimmermann <[e-mail]>
Signed-off-by: Helge Deller <[e-mail]>

drivers/video/fbdev/Kconfig

···
 config FB_WM8505
 	bool "Wondermedia WM8xxx-series frame buffer support"
 	depends on (FB = y) && HAS_IOMEM && (ARCH_VT8500 || COMPILE_TEST)
+	select FB_IOMEM_FOPS
 	select FB_SYS_FILLRECT if (!FB_WMT_GE_ROPS)
 	select FB_SYS_COPYAREA if (!FB_WMT_GE_ROPS)
 	select FB_SYS_IMAGEBLIT