blackfin: SEC: clean up SEC interrupt initialization

Append the SEC IRQ after the IVG6, which is consistent to BF5xx SIC.
Exclude SIC irqchip fucntions from SEC code.
Call handle_fasteoi_irq in SEC error and fault handler.

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: Bob Liu <lliubbo@gmail.com>