target/ppc/cpu_init: Remove "PowerPC" prefix from the CPU list

target/ppc/cpu_init: Remove "PowerPC" prefix from the CPU list

Printing a "PowerPC" in front of each CPU name is not helpful at all:
It is confusing for the users since they don't know whether they
have to specify these letters for the "-cpu" parameter, too, and
it also takes some precious space in the dense output of the CPU
entries. Let's simply remove this now and use two spaces at the
beginning of the lines for the indentation of the entries instead,
and add a "Available CPUs" in the very first line, like most other
target architectures are doing it for their CPU help output already.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>