doc: sandbox: Fix up dependencies

These are out of date. Update them and point to the existing build
instructions to avoid duplication. Add a few that are missing.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/arch/sandbox.rst b/doc/arch/sandbox.rst
index 9e23e16..f8804e1 100644
--- a/doc/arch/sandbox.rst
+++ b/doc/arch/sandbox.rst
@@ -43,11 +43,7 @@
 Prerequisites
 -------------
 
-Here are some packages that are worth installing if you are doing sandbox or
-tools development in U-Boot:
-
-   python3-pytest lzma lzma-alone lz4 python3 python3-virtualenv
-   libssl1.0-dev
+Install the dependencies noted in :doc:`../build/gcc`.
 
 
 Basic Operation
diff --git a/doc/build/gcc.rst b/doc/build/gcc.rst
index c51b3e7..8ffb4e3 100644
--- a/doc/build/gcc.rst
+++ b/doc/build/gcc.rst
@@ -26,8 +26,10 @@
     sudo apt-get install bc bison build-essential coccinelle \
       device-tree-compiler dfu-util efitools flex gdisk liblz4-tool \
       libguestfs-tools libncurses-dev libpython3-dev libsdl2-dev libssl-dev \
-      lzma-alone openssl python3 python3-coverage python3-pyelftools \
-      python3-pytest python3-sphinxcontrib.apidoc python3-sphinx-rtd-theme swig
+      lz4 lzma lzma-alone openssl python3 python3-coverage \
+      python3-pycryptodome python3-pyelftools python3-pytest \
+      python3-sphinxcontrib.apidoc python3-sphinx-rtd-theme python3-virtualenv \
+      swig
 
 SUSE based
 ~~~~~~~~~~