TI ARMv7: Don't use GD before crt0.S has set it

Prior to this change we set the gd pointer early so that we can store
data in it.  This becomes problematic for DM changes as well as being
odd in general.  Re-work the code paths so that we don't need to set the
gd pointer so early and instead can rely upon the normal setting of it.

In order to do this we do need to move certain calls from s_init into
spl_board_init(), mainly preloader_console_init and
save_omap_boot_params.

Tested on: Beaglebone Black, AM43xx GP EVM, Beagleboard, Beagleboard xM,
OMAP5 uEVM, DRA7xx EVM
Signed-off-by: Tom Rini <trini@ti.com>
Tested-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Simon Glass <sjg@chromium.org>