ARM: simplify and fix linker script for TCM

Let's put the TCM stuff in the __init section directly. No need for
a separately freed memory area.

Remove redundant linker sections, as well as comments that were more
confusing than no comments at all. Finally make it XIP compatible by
using LOAD_OFFSET in the section LMA specification.

Signed-off-by: Nicolas Pitre <nico@linaro.org>
Tested-by: Chris Brandt <Chris.Brandt@renesas.com>