FROMLIST: arm64: disable SCS for hypervisor code

Filter out CC_FLAGS_SCS for code that runs at a different exception
level.

Bug: 145210207
Change-Id: I834424fba7aa18598b618891814327ecc2841c6e
(am from https://lore.kernel.org/patchwork/patch/1149062/

)
Suggested-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>