ARM: simplify generation of compressed vmlinux.lds file

As we are now using the C preprocessor, we do not need to use sed to
edit constants in this file, and then pass the resulting file through
the C preprocessor.  Instead, rely solely on the C preprocessor to
rewrite TEXT_START and BSS_ADDR.

Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>