platform: fpga/ariane: Remove redundant plic address macros

All the common PLIC specific macros are already defined in plic.c.

Remove it from platform code. While at it, Fix the other coding style
issues.

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Reviewed-by: Anup Patel <anup.patel@wdc.com>