libpayload/libc: Use size_t for lengths and indices
size_t is the natural integer type for strlen() and array indices, and
this fixes several integer conversion and sign comparison warnings.
Change-Id: I5658b19f990de4596a602b36d9533b1ca96ad947
Signed-off-by: Jacob Garber <jgarber1@ualberta.ca>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/33794
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>