am33xx/omap: Move save_omap_boot_params to omap-common/boot-common.c

We need to call the save_omap_boot_params function on am33xx/ti81xx and
other newer TI SoCs, so move the function to boot-common.  Only OMAP4+
has the omap_hw_init_context function so add ifdefs to not call it on
am33xx/ti81xx.  Call save_omap_boot_params from s_init on am33xx/ti81xx
boards.

Reviewed-by: R Sricharan <r.sricharan@ti.com>
Signed-off-by: Tom Rini <trini@ti.com>