[PPC] Use cpu setup routines from cpu_setup_44x.S for ARCH=ppc

Commit 8112753b made 44x in
ARCH=powerpc builds use cpu setup routines in cpu_setup_44x.S,
but didn't make a similar change for ARCH=ppc, and consequently
the ARCH=ppc builds fail with undefined symbols (since both use
the same cputable.c).

This fixes it by including cpu_setup_44x.S in the ARCH=ppc builds,
and by taking out the now-redundant FPU initialization in
arch/ppc/kernel/head_44x.S.

Signed-off-by: Paul Mackerras <paulus@samba.org>