x86: add genisoimage and xorrisofs as alternatives to mkisofs

Some system not have mkisofs, but have genisoimage or
xorrisofs. They have compatable options for mkisofs,
so let them as alternatives to mkisofs.

Signed-off-by: 李国 <uxgood.org@gmail.com>

target/linux/x86/Makefile

@@ -23,6 +23,9 @@ DEFAULT_PACKAGES += partx-utils mkf2fs e2fsprogs
 
 $(eval $(call BuildTarget))
 
-$(eval $(call $(if $(CONFIG_ISO_IMAGES),RequireCommand,Ignore),mkisofs, \
-   	Please install mkisofs. \
+$(eval $(call $(if $(CONFIG_ISO_IMAGES),SetupHostCommand,Ignore),mkisofs, \
+	Please install mkisofs. , \
+	mkisofs -v 2>&1 , \
+	genisoimage -v 2>&1 | grep genisoimage, \
+	xorrisofs -v 2>&1 | grep xorriso \
 ))