xen/arm64: resync atomics and spinlock asm with Linux

xen/arm64: resync atomics and spinlock asm with Linux

This picks up the changes from Linux commit 3a0310eb369a:
    arm64: atomics: fix grossly inconsistent asm constraints for exclusives

    Our uses of inline asm constraints for atomic operations are fairly
    wild and varied. We basically need to guarantee the following:

      1. Any instructions with barrier implications
         (load-acquire/store-release) have a "memory" clobber

      2. When performing exclusive accesses, the addresing mode is generated
         using the "Q" constraint

      3. Atomic blocks which use the condition flags, have a "cc" clobber

    This patch addresses these concerns which, as well as fixing the
    semantics of the code, stops GCC complaining about impossible asm
    constraints.

    Signed-off-by: Will Deacon <will.deacon@arm.com>
    Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Tim Deegan <tim@xen.org>