KVM: arm64: Move fault context to const structure

KVM: arm64: Move fault context to const structure

In order to make it clearer what gets updated or not during fault
handling, move a set of information that losely represents the
fault context.

This gets populated early, from handle_mem_abort(), and gets passed
along as a const pointer. user_mem_abort()'s signature is majorly
improved in doing so, and kvm_s2_fault loses a bunch of fields.

gmem_abort() will get a similar treatment down the line.

Tested-by: Fuad Tabba <tabba@google.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>