buildman: Update the default settings file

The settings file omits a few lines which are useful for getting every
board building. Add these and update the documentation tool.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/buildman/bsettings.py b/tools/buildman/bsettings.py
index 35bb2c1..f53564e 100644
--- a/tools/buildman/bsettings.py
+++ b/tools/buildman/bsettings.py
@@ -79,10 +79,13 @@
 [toolchain-prefix]
 # name = path to prefix
 # e.g. x86 = /opt/gcc-4.6.3-nolibc/x86_64-linux/bin/x86_64-linux-
+# arc = /opt/arc/arc_gnu_2021.03_prebuilt_elf32_le_linux_install/bin/arc-elf32-
 
 [toolchain-alias]
 # arch = alias
 # Indicates which toolchain should be used to build for that arch
+riscv = riscv32
+sh = sh4
 x86 = i386
 blackfin = bfin
 openrisc = or1k
diff --git a/tools/buildman/buildman.rst b/tools/buildman/buildman.rst
index afdd65d..4851a64 100644
--- a/tools/buildman/buildman.rst
+++ b/tools/buildman/buildman.rst
@@ -199,6 +199,8 @@
    arc = /opt/arc/arc_gnu_2021.03_prebuilt_elf32_le_linux_install/bin/arc-elf32-
 
    [toolchain-alias]
+   riscv = riscv32
+   sh = sh4
    x86: i386
    blackfin: bfin
    openrisc: or1k