ARM: OMAP2+: Fix booting with configs that don't have MFD_SYSCON

With the recent changes omaps have developed a dependency to MFD_SYSCON.
This is used for system control module generic register area and some
clocks.

We do have it selected in omap2plus_defconfig, but targeted config
files may not have it selected. Let's make sure it's selected like
few other ARM platforms are already doing.
Reported-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/mach-omap2/Kconfig

@@ -80,6 +80,7 @@ config ARCH_OMAP2PLUS
 	select GENERIC_IRQ_CHIP
 	select MACH_OMAP_GENERIC
 	select MEMORY
+	select MFD_SYSCON
 	select OMAP_DM_TIMER
 	select OMAP_GPMC
 	select PINCTRL