arm64: scs: use vmapped IRQ and SDEI shadow stacks

Use scs_alloc() to allocate also IRQ and SDEI shadow stacks instead of
using statically allocated stacks.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20201130233442.2562064-3-samitolvanen@google.com


[will: Move CONFIG_SHADOW_CALL_STACK check into init_irq_scs()]
Signed-off-by: Will Deacon <will@kernel.org>