ARM: OMAP2+: Set Kconfig dependencies for PROC_DEVICETREE

Otherwise we get:

warning: (ARCH_OMAP2PLUS) selects PROC_DEVICETREE which has
unmet direct dependencies (OF && PROC_FS && !SPARC)
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/plat-omap/Kconfig

@@ -26,7 +26,7 @@ config ARCH_OMAP2PLUS
 	select GENERIC_IRQ_CHIP
 	select OMAP_DM_TIMER
 	select USE_OF
-	select PROC_DEVICETREE
+	select PROC_DEVICETREE if PROC_FS
 	help
 	  "Systems based on OMAP2, OMAP3 or OMAP4"