SPL: Create arch/arm/lib/spl.c for board_init_f and jump_to_image_linux

In SPL (CONFIG_SPL_FRAMEWORK) board_init_f must setup the stack pointer,
clear the BSS and call board_init_r.  We mark this as weak as some
platforms may need to perform additional initalization at this point.
We provide a gd that we know will be in a usable location, once the BSS
has been cleared to help with this as well.  Finally, we no longer call
relocate_code so remove that from the armv7 version.

Next, both board_init_f and jump_to_image_linux are going to be
inherently arch-specific, so move these versions to arch/arm/lib/spl.c

Signed-off-by: Tom Rini <trini@ti.com>