directfb: disable multi application if no MMU

directfb-fusion uses the madvise() system call which is not available
on no-MMU targets.

It seems it might be possible to simply remove the call to madvise()
(there is only one call) if not available. However, it's probably not
worth the effort, and people working on no-MMU targets can submit a
patch doing that if they are interested.

[Thomas: tweak commit log.]

Signed-off-by: Jérôme Pouiller <jezz@sysmic.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/directfb/Config.in

@@ -12,6 +12,7 @@ if BR2_PACKAGE_DIRECTFB
 config BR2_PACKAGE_DIRECTFB_MULTI
 	bool "directfb multi application"
 	select BR2_PACKAGE_LINUX_FUSION
+	depends on BR2_USE_MMU # madvise()
 	depends on BR2_LINUX_KERNEL
 	help
 	  Enable use of multiple concurrent DirectFB applications