Fixed ARM-software/tf-issues#603
Fixed ARM-software/tf-issues#603

Updated optee_utils.c to fix ARM-software/tf-issues#603 related to the
tee-validate-header bug.

Minor updates to the header valid checking logic. It would never make
sense to have less than 1 image to load so this is now checked.

Changed OPTEE_MAX_IMAGE_NUM to OPTEE_MAX_NUM_IMAGES to clarify its
definition. OPTEE_MAX_IMAGE_NUM sounds like an ID assigned to the last
image to load. OPTEE_MAX_NUM_IMAGES sounds like the maximum number of
images to load.

Signed-off-by: Nathan Menhorn <0f3232ab6d84f2382e8e9e46a38ed1d4946a86a7@xilinx.com>

achingupta/arm-trusted-firmware,achingupta/arm-trusted-firmware