arm64: add Alpine SoC family

This patch introduces ARCH_ALPINE to add the support of the Alpine SoC
family for the arm64 architecture.
Signed-off-by: NAntoine Tenart <antoine.tenart@free-electrons.com>
Acked-by: NArnd Bergmann <arnd@arndb.de>
Signed-off-by: NArnd Bergmann <arnd@arndb.de>

arch/arm64/Kconfig.platforms

 menu "Platform selection"
 
+config ARCH_ALPINE
+	bool "Annapurna Labs Alpine platform"
+	help
+	  This enables support for the Annapurna Labs Alpine
+	  Soc family.
+
 config ARCH_BCM_IPROC
 	bool "Broadcom iProc SoC Family"
 	help