powerpc: Remove klimit

klimit is a global variable initialised at build time with the
value of _end.

This variable is never modified, so _end symbol can be used directly.

Remove klimit.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/9fa9ba6807c17f93f35a582c199c646c4a8bfd9c.1622800638.git.christophe.leroy@csgroup.eu