For AArch32 exceptions, the only information provided about
the cause of an exception is the individual exception type (data
abort, undef, etc), which we store in cs->exception_index. For
AArch64, the CPU provides much more detail about the cause of
the exception, which can be found in the syndrome register.
Create a set of fields in CPUARMState which must be filled in
whenever an exception is raised, so that exception entry can
correctly fill in the syndrome register for the guest.
This includes the information which in AArch32 appears in
the DFAR and IFAR (fault address registers) and the DFSR
and IFSR (fault status registers) for data aborts and
prefetch aborts, since if we end up taking the MMU fault
to AArch64 rather than AArch32 this will need to end up
in different system registers.

This patch does a refactoring which moves the setting of the
AArch32 DFAR/DFSR/IFAR/IFSR from the point where the exception
is raised to the point where it is taken. (This is no change
for cores with an MMU, retains the existing clearly incorrect
behaviour for ARM946 of trashing the MP access permissions
registers which share the c5_data and c5_insn state fields,
and has no effect for v7M because we don't implement its
MPU fault status or address registers.)

As a side effect of the cleanup we fix a bug in the AArch64
linux-user mode code where we were passing a 64 bit fault
address through the 32 bit c6_data/c6_insn fields: it now
goes via the always-64-bit exception.vaddress.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>