uboot-imx

image: Convert the IH_... values to enums

We need to know the number of values of each category (architecture,
compression, OS and image type). To make this value easier to maintain,
convert all values to enums. The count is then automatic.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>