irqchip/riscv-intc: Remove asmlinkage

The two functions riscv_intc_aia_irq() and riscv_intc_irq()
are only called by C functions.

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Anup Patel <anup@brainfault.org>
Link: https://lore.kernel.org/r/20240614151955.1949-1-jszhang@kernel.org