This issue is a collection of patches that implement the design to fix C enumeration implicit casting (https://review.trustedfirmware.org/c/trusted-firmware-m/+/1040) plus various code quality improvement.

The general list of fixes is:

• avoid implicit casting by using matching types, casting or conversion functions
• make explicit that the return value of a function is not used
• remove function return type if not needed
• replace preprocessor if condition by ifdef if only definition is checked
• replace enumerated types not used by preprocessor constants
• fix indentation of code

This issue is a follow-up of T274 (https://developer.trustedfirmware.org/T274).

The concerned patches are:

• https://review.trustedfirmware.org/c/trusted-firmware-m/+/1374/
• https://review.trustedfirmware.org/c/trusted-firmware-m/+/1375/
• https://review.trustedfirmware.org/c/trusted-firmware-m/+/1376/
• https://review.trustedfirmware.org/c/trusted-firmware-m/+/1377/
• https://review.trustedfirmware.org/c/trusted-firmware-m/+/1378/