link: Move x86-ism out of the linker script

link: Move x86-ism out of the linker script

... in preparation to reuse it for all architectures.  In order to keep
various parts of the linker script all together, use a multi-include file with
header and footer delineations.

While moving things, drop the alignment check for the two stacks.  Neither
need page alignment architecturally.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>