Blackfin: SMP: enable HAVE_LEGACY_PER_CPU_AREA

The current Blackfin SMP code relies on the legacy cpu area code, so
select it until we port things to the newer code.
Signed-off-by: Graf Yang <graf.yang@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>

arch/blackfin/Kconfig

@@ -258,6 +258,10 @@ config IRQ_PER_CPU
 	depends on SMP
 	default y
 
+config HAVE_LEGACY_PER_CPU_AREA
+	def_bool y
+	depends on SMP
+
 config BF_REV_MIN
 	int
 	default 0 if (BF51x || BF52x || (BF54x && !BF54xM))