powerpc/emulator: Fix compilation with recent versions of GCC

New versions of GCC (e.g. version 11.2 from Fedora 34) refuse to compile
assembly with the lswx and lswi mnemonics in little endian mode since the
instruction is only allowed in big endian mode, thus emulator.c cannot be
compiled anymore. Re-arrange the tests a little bit to use hand-crafted
instructions in little endian mode to fix this issue. Additionally, the lswx
and lswi instructions generate an alignment exception with recent versions
of QEMU, too (see https://gitlab.com/qemu-project/qemu/-/commit/5817355ed0

),
so we can turn the report_xfail() into proper report() statements now.

Message-Id: <20211026061532.117368-1-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>