sparc,sparc64: unify Makefile

To unify Makefile for sparc and sparc64 a few other steps was needed:
1) separate defconfig files for sparc and sparc64 is required,
   so locate these in arch/sparc/configs
2) removoval of hack in toplevel Makefile to deal with that
   headers was in a separate directory compared to the rest

The unification of the Makefile required usage of several

    foo-$(CONFIG_SPARCnn) +=

due to a few directories pending unification.
This will be cleaned up when we unify the remaining directories.

Included in this patch are the deletion of a few files in
sparc64 as they are no longer needed: Makefile + Kconfig.
arch/sparc64/ will after this patch is applied only
have four directories (prom, lib, kernel, boot)

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: David S. Miller <davem@davemloft.net>