Platform: PSoC64: Tweak SMPU configuration

Remove protection from the secondary secure image to support
upgrading it.
Re-purpose SMPU1 to cover just the ITS part of flash.
Re-purpose SMPU2 to cover just the NV Counters in flash.
Re-purpose SMPU3 to cover just the SST part of flash.
This also removes protection from the unused space in flash.

Change-Id: Id9517b85db426b760069d7133651bd362d21eba9
Signed-off-by: Chris Brand <chris.brand@cypress.com>