irqchip/irq-csky-mpintc: Add triger type and priority

Support 4 triger types:
 - IRQ_TYPE_LEVEL_HIGH
 - IRQ_TYPE_LEVEL_LOW
 - IRQ_TYPE_EDGE_RISING
 - IRQ_TYPE_EDGE_FALLING

Support 0-255 priority setting for each irq.

Changelog:
 - Fixup this_cpu_read() preempted problem.
 - Optimize the coding style.

Signed-off-by: Guo Ren <ren_guo@c-sky.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>