ANDROID: kbuild: disable SCS by default in allmodconfig

4.14 doesn't support checking for clang in Kconfig, so change
CONFIG_SHADOW_CALL_STACK into a choice, which defaults to SCS
being disabled.

Bug: 145297810
Fixes: a7f21069 ("FROMLIST: add support for Clang's Shadow Call Stack (SCS)")
Change-Id: I4673d598b11d92a873401fa08301fabd8ae71a01
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>