arm64: Always use REFCOUNT_FULL

As discussed at the Linux Security Summit, arm64 prefers to use
REFCOUNT_FULL by default. This enables it for the architecture.

Cc: hw.likun@huawei.com
Cc: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: NKees Cook <keescook@chromium.org>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

arch/arm64/Kconfig

@@ -119,6 +119,7 @@ config ARM64
 	select PCI_ECAM if ACPI
 	select POWER_RESET
 	select POWER_SUPPLY
+	select REFCOUNT_FULL
 	select SPARSE_IRQ
 	select SYSCTL_EXCEPTION_TRACE
 	select THREAD_INFO_IN_TASK