asm/scs.h is no longer needed by the core code, so remove a redundant
header inclusion and update the stale Kconfig text.
Tested-by: NSami Tolvanen <samitolvanen@google.com>
Reviewed-by: NMark Rutland <mark.rutland@arm.com>
Signed-off-by: NWill Deacon <will@kernel.org>