UPSTREAM: arm64: Store struct thread_info in sp_el0

UPSTREAM: arm64: Store struct thread_info in sp_el0

There is need for figuring out how to manage struct thread_info data when
IRQ stack is introduced. struct thread_info information should be copied
to IRQ stack under the current thread_info calculation logic whenever
context switching is invoked. This is too expensive to keep supporting
the approach.

Instead, this patch pays attention to sp_el0 which is an unused scratch
register in EL1 context. sp_el0 utilization not only simplifies the
management, but also prevents text section size from being increased
largely due to static allocated IRQ stack as removing masking operation
using THREAD_SIZE in many places.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Jungseok Lee <jungseoklee85@gmail.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 6cdf9c7ca687e01840d0215437620a20263012fc)
Signed-off-by: Jeff Vander Stoep <jeffv@google.com>
Change-Id: I53c9f44a0772b8649f302a65a7a6519d8eebcb91