irqchip/lpc32xx: Switch to dynamic chip name output

Instead of overriding the name field with the device name, use
the relevant callback. This allows us to make the irq_chip structure
const.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20220209162607.1118325-5-maz@kernel.org