arch: arm: vector_table: Support vector table soft relay

For SoCs that don't support vector table relocation in hardware, may not
support bootloader like mcuboot.

We introduce a way to relocate vector table in software by forwarding
the control of incoming IRQs to a new vector table which address is save
at fixed SRAM address.

User can change the data in that fixed SRAM address in order to relocate
vector table in software way.

Signed-off-by: Ding Tao <miyatsu@qq.com>