target-arm: aarch64: add support for ADR and ADRP

this adds support for the instructions described in:
C3.4.6 PC-rel. addressing (ADR and ADRP).

Signed-off-by: Alexander Graf <agraf@suse.de>

[claudio: adapted to new decoder structure]

Signed-off-by: Claudio Fontana <claudio.fontana@linaro.org>

from Alexander Graf <agraf@suse.de> aarch64 series 26/60