ARM: remove obsolete Makefile.boot infrastructure

ARM: remove obsolete Makefile.boot infrastructure

There are a number of old Makefile.boot files that remain from the
multiplatform conversion, and three that are still in use.

These provide the "ZRELADDR", "PARAMS_PHYS" and "INITRD_PHYS" values
that are platform specific. It turns out that we can generally just
derive this from information that is available elsewhere:

- ZRELADDR is normally detected at runtime with the
  CONFIG_AUTO_ZRELADDR flag, but also needed to be passed to
  for 'make uImage'. In a multiplatform kernel, one always has
  to pass this as the $(LOADADDR) variable, but in the StrongARM
  kernels we can derive it from the sum of $(CONFIG_PHYS_OFFSET)
  and $(TEXT_OFFSET) that are already known.

- PARAMS_PHYS and INITRD_PHYS are only used for bootpImage, which
  in turn is only used for the pre-ATAGS 'param_struct' based boot
  interface on StrongARM based machines with old boot loaders.
  They can both be derived from CONFIG_PHYS_OFFSET and a machine
  specific offset for the initrd, so all of the logic for these
  can be part of arch/arm/boot/bootp/Makefile.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>