ARM: linker script: factor out some common definitions between XIP and non-XIP

Lots of duplications between vmlinux.lds.S and vmlinux-xip.lds.S.
This may lead to one file being updated but not the other. For example,
SOFTIRQENTRY_TEXT and HYPERVISOR_TEXT were missing from the XIP version.

This creates vmlinux.lds.h where a bunch of common defines are moved.

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