isr_tables: adopt _irq_vector_table for using on 64bit architectures

As of today generic _irq_vector_table is used only on 32bit
architectures and 64bit architectures have their own implementation.
Make vectors size adjustable by using uintptr_t instead of uint32_t
for vectors.

The ARCv3 64 bit HS6x processors are going to be first users for
that.

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>