tools: Remove CONFIG_SYS_TEXT_BASE in Makefile

This define is not used in tools sources and can be removed
to avoid unnecessary link between tools and defconfig

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>