target/ppc: Fix migration of CPUs with TLB_EMB TLB type

target/ppc: Fix migration of CPUs with TLB_EMB TLB type

In vmstate_tlbemb a cut-and-paste error meant we gave
this vmstate subsection the same "cpu/tlb6xx" name as
the vmstate_tlb6xx subsection. This breaks migration load
for any CPU using the TLB_EMB CPU type, because when we
see the "tlb6xx" name in the incoming data we try to
interpret it as a vmstate_tlb6xx subsection, which it
isn't the right format for:

 $ qemu-system-ppc -drive
 if=none,format=qcow2,file=/home/petmay01/test-images/virt/dummy.qcow2
 -monitor stdio -M bamboo
 QEMU 9.0.92 monitor - type 'help' for more information
 (qemu) savevm foo
 (qemu) loadvm foo
 Missing section footer for cpu
 Error: Error -22 while loading VM state

Correct the incorrect vmstate section name. Since migration
for these CPU types was completely broken before, we don't
need to care that this is a migration compatibility break.

This affects the PPC 405, 440, 460 and e200 CPU families.

Cc: qemu-stable@nongnu.org
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2522
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Arman Nabiev <nabiev.arman13@gmail.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>