[ARC][committed] Update int_vector_base aux register.

INT_VECTOR_BASE auxiliary register is available across all ARC
architectures.

xxxx-xx-xx  Claudiu Zissulescu <claziss@gmail.com>

	* arc-regs.h (int_vector_base): Make it available for all ARC
	CPUs.

Signed-off-by: Claudiu Zissulescu <claziss@gmail.com>