BACKPORT: arm64: Use __pa_symbol for kernel symbols

(cherry-pick from commit 2077be67)

__pa_symbol is technically the marcro that should be used for kernel
symbols. Switch to this as a pre-requisite for DEBUG_VIRTUAL which
will do bounds checking.

Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Bug: 20045882
Bug: 63737556
Change-Id: Ibef89e5935c9562fa69e946778c705636c1ca61e