arch/common: Mark interrupt tables const when !DYNAMIC_INTERRUPTS

When not using dynamic interrupt mapping, various interrupt tables are
configured to be stored in read-only memory in the linker script.. Mark
them const so that the linker doesn't complain.

This affects _sw_isr_table, _irq_vector_table, and z_shared_sw_isr_table in
arch/common along with _VectorTable in arch/arc.

Signed-off-by: Keith Packard <keithp@keithp.com>