scripts: use local cpu count to build

Build faster by using all available cores by default
The xtensa script claims it used infinite build threads when j was not
specified but it was actually falling back to 1.

Signed-off-by: Curtis Malainey <cujomalainey@google.com>

scripts/host-build-all.sh

@@ -13,5 +13,5 @@ cmake -DBUILD_HOST=ON \
 	-DCMAKE_VERBOSE_MAKEFILE=ON \
 	..
 
-make -j4
+make -j$(nproc --all)
 make install

scripts/xtensa-build-all.sh

@@ -4,7 +4,7 @@ SUPPORTED_PLATFORMS=(byt cht bdw hsw apl cnl sue icl skl kbl)
 BUILD_ROM=no
 BUILD_DEBUG=no
 BUILD_FORCE_UP=no
-BUILD_JOBS=1
+BUILD_JOBS=$(nproc --all)
 BUILD_JOBS_NEXT=0
 
 PATH=$pwd/local/bin:$PATH
@@ -19,7 +19,8 @@ then
 	echo "       [-u] Force UP ARCH"
 	echo "       [-d] Enable debug build"
 	echo "       [-c] Configure defconfig"
-	echo "       [-j [n]] Set number of make build jobs. Infinite jobs with no arg."
+	echo "       [-j [n]] Set number of make build jobs." \
+		"Jobs=#cores when no flag. Inifinte when no arg."
 	echo "       Supported platforms ${SUPPORTED_PLATFORMS[@]}"
 else
 	# parse the args