feat[build]: Add --toolchain to config toolchain for linux

for example
./make-Makefiles.bash --toolchain gcc-arm-10.3-2021.07-x86_64-aarch64-none-linux-gnu/bin/aarch64-none-linux-gnu-

Change-Id: I4804b1e1759aab04f715d826fbe412087298cb89
Signed-off-by: Yandong Lin <yandong.lin@rock-chips.com>

build/linux/opt_proc.sh

@@ -23,10 +23,16 @@ while [ $# -gt 0 ]; do
     case $1 in
         --help | -h)
             echo "Execute make-Makefiles.sh in *arm/* or *aarch64/* with some args."
+            echo "  use --toolchain to set toolchain e.g. --toolchain path/aarch64-none-linux-gnu-"
             echo "  use --rebuild to rebuild after clean"
             echo "  use --clean to clean all build file"
             exit 1
             ;;
+        --toolchain)
+            TOOLCHAIN=$2
+            echo "toolchain: ${TOOLCHAIN}"
+            shift
+            ;;
         --rebuild)
             ${MAKE_PROGRAM} clean
             if [ -f "CMakeCache.txt" ]; then