spl: Convert nand to spl_load

spl: Convert nand to spl_load

This converts the nand load method to use spl_load. nand_page_size may not
be valid until after nand_spl_load_image is called (see e.g. fsl_ifc_spl),
so we set bl_len in spl_nand_read. Since spl_load reads the header for us,
we can remove that argument from spl_nand_load_element.

There are two possible regressions which could result from this commit.
First, we ask for a negative address from spl_get_load_buffer. That is,
instead of

	header = spl_get_load_buffer(0, sizeof(*header));

we do

	header = spl_get_load_buffer(-sizeof(*header), sizeof(*header));

this could cause a problem if spl_get_load_buffer does not return valid
memory for negative offsets. Second, we now set bl_len for legacy images.
This can cause memory up to a bl_len - 1 before the image load address to
be written, which might not have been the case before. If this turns out to
be a problem, we can add an option for a bounce buffer.

We can't load FITs with external data with SPL_LOAD_FIT_FULL, so disable the
test in that case. No boards enable SPL_NAND_SUPPORT and SPL_LOAD_FIT_FULL, so
this is not a regression.

Signed-off-by: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>