spl: Convert CONFIG_SPL_ABORT_ON_RAW_IMAGE into a positive option

CONFIG_SPL_ABORT_ON_RAW_IMAGE causes SPL to abort and move on when it
encounters RAW images, express this same functionality as a positive
option enabling support for RAW images: CONFIG_SPL_RAW_IMAGE_SUPPORT

Also move uses of this to defconfigs.

Signed-off-by: Andrew F. Davis <afd@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
[trini: Rework Kconfig logic a little, move to common/spl/Kconfig]
Signed-off-by: Tom Rini <trini@konsulko.com>