target-arm: helper.c: RAZ REVIDR cp register

Guests should be able to read REVIDR without suffering an abort. Just
RAZ the REVIDR register.

Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
target-arm/helper.c: OMAP/StrongARM cp15 crn=0 cleanup

The if block detecting OMAP/StrongARM modifies the id_cp_reginfo
.access fields in place. So there is no need to replicate the call
to define_arm_cp_reg. Dropped, and let the OMAP case fall through
to the normal behaviour after the in-place modification.

Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
target-arm/helper.c: Implement MIDR aliases

The MIDR CP (cp15, CRn=0, opc1=0, CRm=0) Has a number of aliases with
varying values of opc2. Implemented.

Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>