Make the IRQ Table extern definable.

Make the IRQ Table extern definable.

This makes the IRQ-table extern definable. With this it is possible to define Interrupt Service Routines in the CMSIS way with week defined IRQ-Routines which can be overridden in the application code.

Example:
// …
__attribute__ ((weak, alias("InteruptDefaultHandler"))) void CoreTimer_IRQHandler (void);
// …

IRQHandler_t IRQTable [IRQ_GIC_LINE_COUNT] =
{
// …
CoreTimer_IRQHandler
// …
};

In Addition a default IRQ-Handler is implemented which calls the Interrupt-Service-Routine.