target/ppc: Fix e6500 boot

target/ppc: Fix e6500 boot

When Altivec support was added to the e6500 kernel in 2012[1], the
QEMU code was not changed, so we don't register the VPU/VPUA
exceptions for the e6500:

  qemu: fatal: Raised an exception without defined vector 73

Note that the error message says 73, instead of 32, which is the IVOR
for VPU. This is because QEMU knows only knows about the VPU interrupt
for the 7400s. In theory, we should not be raising _that_ VPU
interrupt, but instead another one specific for the e6500.

We unfortunately cannot register e6500-specific VPU/VPUA interrupts
because the SPEU/EFPDI interrupts also use IVOR32/33. These are
present only in the e500v1/2 versions. From the user manual:

e500v1, e500v2: only SPEU/EFPDI/EFPRI
e500mc, e5500:  no SPEU/EFPDI/EFPRI/VPU/VPUA
e6500:          only VPU/VPUA

So I'm leaving IVOR32/33 as SPEU/EFPDI, but altering the dispatch code
to convert the VPU #73 to a #32 when we're in the e6500. Since the
handling for SPEU and VPU is the same this is the only change that's
needed. The EFPDI is not implemented and will cause an abort. I don't
think it worth it changing the error message to take VPUA into
consideration, so I'm not changing anything there.

This bug was discussed in the thread:
https://lists.gnu.org/archive/html/qemu-ppc/2021-06/msg00222.html

1- https://git.kernel.org/torvalds/c/cd66cc2ee52

Reported-by: <mario@locati.it>
Signed-off-by: Fabiano Rosas <farosas@linux.ibm.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Message-Id: <20211213133542.2608540-1-farosas@linux.ibm.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>