Add ARM64 to the legend of architectures.  It's already used in several
places in kernel-parameters.txt.
Suggested-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
        APIC    APIC support is enabled.
        APM     Advanced Power Management support is enabled.
        ARM     ARM architecture is enabled.
+       ARM64   ARM64 architecture is enabled.
        AX25    Appropriate AX.25 support is enabled.
        CLK     Common clock infrastructure is enabled.
        CMA     Contiguous Memory Area support is enabled.