arm64: Enable CONFIG_64BIT for static analysis

In the Makefile there is a line that says this:

    # the checker needs the correct machine size
    CHECKFLAGS += $(if $(CONFIG_64BIT),-m64,-m32)

Set CONFIG_64BIT for ARM64 so that we pass -m64 to the static checkers
instead of -m32.

Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>

arch/arm/Kconfig

@@ -6,6 +6,7 @@ config SYS_ARCH
 
 config ARM64
 	bool
+	select 64BIT
 	select PHYS_64BIT
 	select SYS_CACHE_SHIFT_6
 	imply SPL_SEPARATE_BSS