kernel: avoid Boolean-to-integer type casts

[tychofrei02]

Avoid casting expression to an inappropriate essential type.

This corresponds to following coding guideline:

The value of an expression should not be cast to an inappropriate essential type

This PR is part of the enhancement issue #48002 which port the coding guideline fixes done by BUGSENG on the https://github.com/zephyrproject-rtos/zephyr/tree/v2.7-auditable-branch back to main

The commit in this PR is a subset of the original auditable-branch commit:
7eadb9c

[andyross]

FWIW this one is an artifact of the syscall generation script not being able to represent booleans in the generated marshal code. Probably not worth demanding a real fix in a MISRA PR, but in case someone feels inspired...