common: always compile fixup_cmdtable()

With our optimization settings the linker eliminates unused functions.

But for debugging it is better to compile with -Og or -O0. With -O0
compiling the sandbox fails due to the missing function fixup_cmdtable()
called by dm_reloc() and others.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>