linux-user, ppc: mftbl can be used by user application

In qemu-linux-user, when calling gethostbyname2(),
it was hanging in .__res_nmkquery.

(gdb) bt
0 in .__res_nmkquery () from /lib64/libresolv.so.2
1 in .__libc_res_nquery () from /lib64/libresolv.so.2
2 in .__libc_res_nsearch () from /lib64/libresolv.so.2
3 in ._nss_dns_gethostbyname3_r () from /lib64/libnss_dns.so.2
4 in ._nss_dns_gethostbyname2_r () from /lib64/libnss_dns.so.2
5 in .gethostbyname2_r () from /lib64/libc.so.6
6 in .gethostbyname2 () from /lib64/libc.so.6

.__res_nmkquery() is:

...
do { RANDOM_BITS (randombits); } while ((randombits & 0xffff) == 0);
...

<.__res_nmkquery+112>:	mftbl   r11
<.__res_nmkquery+116>:	clrlwi  r10,r11,16
<.__res_nmkquery+120>:	cmpwi   cr7,r10,0
<.__res_nmkquery+124>:	beq     cr7,<.__res_nmkquery+112>

but as mftbl (Move From Time Base Lower) is not implemented,
r11 is always 0, so we have an infinite loop.

This patch fills the Time Base register with cpu_get_real_ticks().

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Alexander Graf <agraf@suse.de>