arm64: Use larger stacks when KASAN is selected

arm64: Use larger stacks when KASAN is selected

AddressSanitizer instrumentation can significantly bloat the stack, and
with GCC 7 this can result in stack overflows at boot time in some
configurations.

We can avoid this by doubling our stack size when KASAN is in use, as is
already done on x86 (and has been since KASAN was introduced).
Regardless of other patches to decrease KASAN's stack utilization,
kernels built with KASAN will always require more stack space than those
built without, and we should take this into account.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
(cherry picked from commit b02faed15d86f846b0f23f47b92e0782baa873ed)

CVE-2017-5753
CVE-2017-5715
CVE-2017-5754

Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>
Acked-by: Brad Figg <brad.figg@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>