MIPS: EMMA2RH: Remove useless CPU_IRQ_BASE

For historical reasons, we used to put MIPS CPU IRQs behind SoC-specific
IRQs in the queue, and have been using CPU_IRQ_BASE as MIPS_CPU_IRQ_BASE.
In recent years, however, we've brought it back to normal order, and now
CPU_IRQ_BASE just redefines the generic MIPS_CPU_IRQ_BASE.

At the same time, NUM_CPU_IRQ is also removed as useless.

Signed-off-by: Shinya Kuribayashi <shinya.kuribayashi.px@renesas.com>
To: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/1387/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>