gpio: pl061: remove confusing naming

Drop the " gpio" suffix after the pl061 irq_chip name:
this is only confusing: an irqchip name should be a single,
short, simple string that looks nice in /proc/interrupts.

Drop the nameing of each individual IRQ to "pl061" - I
think this naming function is for naming the IRQ line,
not for boilerplating them all with the name of the
parent controller, which is already known from the
.name field of the irq_chip.

Cc: Haojian Zhuang <haojian.zhuang@linaro.org>
Cc: Deepak Sikri <deepak.sikri@st.com>
Acked-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>