target-s390x: use softmmu functions for mvcp/mvcs

mvcp and mvcs helper get access to the physical memory by a call to
mmu_translate for the virtual to real conversion and then using ldb_phys
and stb_phys to physically access the data. In practice this is quite
slow because it bypasses the QEMU softmmu TLB and because stb_phys calls
try to invalidate the corresponding memory for each access.

Instead use cpu_ldb_{primary,secondary} for the loads and
cpu_stb_{primary,secondary} for the stores. Ideally this should be
further optimized by a call to memcpy, but that already improves the
boot time of a guest by a factor 1.8.

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Alexander Graf <agraf@suse.de>
