arm64: disable Broadcom Vulcan platform

Disable the option ARCH_VULCAN as a step towards deleting it entirely.
There is still a reference in the kernel tree for ARCH_VULCAN, so we
have to keep the config option around until that reference is removed.
Signed-off-by: Jayachandran C <jnair@caviumnetworks.com>
Signed-off-by: Olof Johansson <olof@lixom.net>

arch/arm64/Kconfig.platforms

@@ -225,10 +225,7 @@ config ARCH_VEXPRESS
 	  Express).
 
 config ARCH_VULCAN
-	bool "Broadcom Vulcan SOC Family"
-	select GPIOLIB
-	help
-	  This enables support for Broadcom Vulcan SoC Family
+	def_bool n
 
 config ARCH_XGENE
 	bool "AppliedMicro X-Gene SOC Family"