lib/asm-offsets - make GD_RELOCADDR, GD_RELOC_OFF & GD_START_ADDR_SP available for all architectures

GD_RELOCADDR, GD_RELOC_OFF & GD_START_ADDR_SP are generic members of
global data structure so why don't we allow architectures other than ARM
to use it.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Tom Rini <trini@ti.com>
Acked-by: Simon Glass <sjg@chromium.org>