UPSTREAM: arm64: Add do_softirq_own_stack() and enable irq_stacks

UPSTREAM: arm64: Add do_softirq_own_stack() and enable irq_stacks

entry.S is modified to switch to the per_cpu irq_stack during el{0,1}_irq.
irq_count is used to detect recursive interrupts on the irq_stack, it is
updated late by do_softirq_own_stack(), when called on the irq_stack, before
__do_softirq() re-enables interrupts to process softirqs.

do_softirq_own_stack() is added by this patch, but does not yet switch
stack.

This patch adds the dummy stack frame and data needed by the previous
stack tracing patches.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Bug: 30369029
Patchset: per-cpu-irq-stack

(cherry picked from commit 8e23dacd12a48e58125b84c817da50850b73280a)
Signed-off-by: Jeff Vander Stoep <jeffv@google.com>
Change-Id: I9f79437af3da0398cb12e7afd1aa9f473f59b2e6