RSS: Support higher MCUBOOT_IMAGE_NUMBER

Currently, TF-M does not support for more than 4 MCUBOOT_IMAGE_NUMBER
and changing the image number requires lots of changes to the code.
This patch allows to increase this number (up to the maximum allowed)
and reduces the amount of code changes needed when changing the value.

Signed-off-by: Arnold Gabriel Benedict <arnoldgabriel.benedict@arm.com>
Change-Id: If3ca3d7b64595a6cedc4f5bb3d6b076e408af6f3
6 files changed