We use the switch CONFIG_SUPPORT_EMMC_BOOT today to enable some
additional features of the eMMC boot partitions.  Add support for being
told that we have booted from one of these partitions to the spl
framework and implement this on TI OMAP/related.

Cc: Pantelis Antoniou <panto@antoniou-consulting.com>
Signed-off-by: Tom Rini <trini@ti.com>
Signed-off-by: Pantelis Antoniou <panto@antoniou-consulting.com>