configure: Enable threading on all ppc and mips linux-user targets

Though threading (target_nptl) was enabled on the base PPC and MIPS
targets, it wasn't enabled for the variants mipsn32, mipsn32el,
mips64, mips64el, ppc64 or ppc46abi32 (probably an oversight).
Enable threading consistently on all these targets.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NRichard Henderson <rth@twiddle.net>
Reviewed-by: NRichard Henderson <rth@twiddle.net>
Signed-off-by: NRiku Voipio <riku.voipio@linaro.org>

configure

@@ -4225,13 +4225,11 @@ case "$target_name" in
     TARGET_BASE_ARCH=mips
     echo "TARGET_ABI_MIPSN32=y" >> $config_target_mak
     echo "TARGET_ABI32=y" >> $config_target_mak
-    target_nptl="no"
   ;;
   mips64|mips64el)
     TARGET_ARCH=mips64
     TARGET_BASE_ARCH=mips
     echo "TARGET_ABI_MIPSN64=y" >> $config_target_mak
-    target_nptl="no"
   ;;
   moxie)
   ;;
@@ -4252,7 +4250,6 @@ case "$target_name" in
     TARGET_BASE_ARCH=ppc
     TARGET_ABI_DIR=ppc
     gdb_xml_files="power64-core.xml power-fpu.xml power-altivec.xml power-spe.xml"
-    target_nptl="no"
   ;;
   ppc64abi32)
     TARGET_ARCH=ppc64
@@ -4260,7 +4257,6 @@ case "$target_name" in
     TARGET_ABI_DIR=ppc
     echo "TARGET_ABI32=y" >> $config_target_mak
     gdb_xml_files="power64-core.xml power-fpu.xml power-altivec.xml power-spe.xml"
-    target_nptl="no"
   ;;
   sh4|sh4eb)
     TARGET_ARCH=sh4