ARM: spectre: add Kconfig symbol for CPUs vulnerable to Spectre

Add a Kconfig symbol for CPUs which are vulnerable to the Spectre
attacks.
Signed-off-by: NRussell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: NFlorian Fainelli <f.fainelli@gmail.com>
Boot-tested-by: NTony Lindgren <tony@atomide.com>
Reviewed-by: NTony Lindgren <tony@atomide.com>
Acked-by: NMarc Zyngier <marc.zyngier@arm.com>

arch/arm/mm/Kconfig

@@ -415,6 +415,7 @@ config CPU_V7
 	select CPU_CP15_MPU if !MMU
 	select CPU_HAS_ASID if MMU
 	select CPU_PABRT_V7
+	select CPU_SPECTRE if MMU
 	select CPU_THUMB_CAPABLE
 	select CPU_TLB_V7 if MMU
 
@@ -826,6 +827,9 @@ config CPU_BPREDICT_DISABLE
 	help
 	  Say Y here to disable branch prediction.  If unsure, say N.
 
+config CPU_SPECTRE
+	bool
+
 config TLS_REG_EMUL
 	bool
 	select NEED_KUSER_HELPERS