um: allow disabling NO_IOMEM

Adjust the kconfig a little to allow disabling NO_IOMEM in UML. To
make an "allyesconfig" with CONFIG_NO_IOMEM=n build, adjust a few
Kconfig things elsewhere and add dummy asm/fb.h and asm/vga.h files.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
diff --git a/arch/um/Kconfig b/arch/um/Kconfig
index 57cfd9a..e72b4b3 100644
--- a/arch/um/Kconfig
+++ b/arch/um/Kconfig
@@ -27,6 +27,10 @@
 	default y
 
 config NO_IOMEM
+	bool "disable IOMEM" if EXPERT
+	default y
+
+config NO_IOPORT_MAP
 	def_bool y
 
 config ISA