target/ppc: code motion from translate_init.c.inc to gdbstub.c

All the code related to gdb has been moved from translate_init.c.inc
file to the gdbstub.c file, where it makes more sense.

Version 4 fixes the omission of internal.h in gdbstub, mentioned in
<87sg3d2gf5.fsf@linux.ibm.com>, and the extra blank line.

Signed-off-by: Bruno Larsen (billionai) <bruno.larsen@eldorado.org.br>
Suggested-by: Fabiano Rosas <farosas@linux.ibm.com>
Message-Id: <20210426184706.48040-1-bruno.larsen@eldorado.org.br>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>