tests: kernel: arm_irq_vector_table: refactor custom IRQ settings

In order to make this test easy to extend for additional
Cortex-M-based platforms, we apply the following minor
refactoring to the test:
- we introduce the _ISR_OFFSET macro to denote the offset
  inside the interrupts' vector table (starting from IRQ
  line 0) of the first manually installed ISR.
- we move the asserts that ensure the validity of the custom
  vector table to build-time and place them in the beginning
  of the text, outside source code.

Signed-off-by: Ioannis Glaropoulos <Ioannis.Glaropoulos@nordicsemi.no>
1 file changed