[CRIS] Remove links from CRIS build

Remove the links to architecture and machine dependent directories
(boot, lib, drivers, arch, mach)

The links were created and used mostly from the arch/cris/Makefile,
so why not dispense with them altogether?
Changed $(ARCH) to "cris" in Makefile, it is easier to read this way.

The CRISv32 head.S common files for the kernel and compressed images
needed to be modified to use ifdefs instead of using the now removed
mach link. Since there are only two versions, this is not a huge loss
in readability.

The link to vmlinux.lds.S is also replaced with a merged version
which uses ifdefs to select the correct layout.
System.map before and after are identical.

Signed-off-by: Jesper Nilsson <jesper.nilsson@axis.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>