image: Rename fit_image_check_hashes() to fit_image_verify()

image: Rename fit_image_check_hashes() to fit_image_verify()

This is the main entry point to the FIT image verification code. We will
be using it to handle image verification with signatures, so rename the
function.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Marek Vasut <marex@denx.de>