irqchip/mbigen: rename register marcros

hulk inclusion
category: feature
bugzilla: 46791
CVE: N/A

-------------------------------------------------

A MBIGEN can also be used for generating SPIs, so let's
rename register macros to make them more resonable.

The first 64-pins of MBIGEN is used by SPIs, so rename
RESERVED_IRQ_PER_MBIGEN_CHIP to SPI_NUM_PER_MBIGEN_CHIP
and change the comment for this marcro.

Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Hanjun Guo <guohanjun@huawei.com>
Signed-off-by: zhangyi (F) <yi.zhang@huawei.com>
Acked-by: Xie XiuQi <xiexiuqi@huawei.com>
Signed-off-by: Chen Jun <chenjun102@huawei.com>