arch: arm: correct fault address logging In ARMv7-M (and ARMv8-M) architecture it is implementation defined whether separate MMFAR and BFAR are implemented. This commit ensures that we always get the true faulting address displayed in case of MemManage- or BusFault. Signed-off-by: Ioannis Glaropoulos <Ioannis.Glaropoulos@nordicsemi.no>