target/ppc: Fix nip on power management instructions

target/ppc: Fix nip on power management instructions

Those instructions currently raise an exception from within
the helper. This tends to result in a bogus nip value in
the env context (typically the beginning of the TB). Such
a helper needs a gen_update_nip() first.

This fixes it with a different approach which is to throw the
exception from translate.c instead of the helper using
gen_exception_nip() which does the right thing. Exception
EXCP_HLT is also used instead of POWERPC_EXCP_STOP to effectively
exit from the CPU execution loop.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
[clg : modified the commit log to comment the use of EXCP_HLT instead
       of POWERPC_EXCP_STOP]
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Message-Id: <20190215161648.9600-2-clg@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>