ARM: vmlinux*.lds.S: some decruftification

Remove stuff from vmlinux.lds.S that is relevant only to the XIP build,
and stuff from vmlinux-xip.lds.S related to self-modifying code that
makes no sense in the XIP case.

Signed-off-by: Nicolas Pitre <nico@linaro.org>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: Chris Brandt <Chris.Brandt@renesas.com>