Checks for support for VTOR in cmsis_nvic.c

The compiler checks in cmsis_nvic.c have been written such that it is difficult to add any new platforms without VTOR presence. The code only wants ensure that the NVIC routines are present in the implementation but this is linked to VTOR presence based on core type which is not necessary. Instead, if the compiler directives are about the presence of NVIC routine itself, i.e. not the processor arch., then the compile time option can be easily configurable and allows future extension.

This is affecting ongoing work.

Start in cmsis_nvic.c by reading the compiler checks that tie NVIC routines to VTOR and core type. Trace which directives determine whether the NVIC routines are available, then separate those checks from processor architecture and VTOR presence. Done means future platforms can configure NVIC routine support without requiring VTOR; no test file is named.

Written by the indexing model from the issue text.