ARM: 9298/1: Drop custom mdesc->handle_irq()

ARM exclusively uses GENERIC_IRQ_MULTI_HANDLER, so at some point
set_handle_irq() needs to be called to handle system-wide
interrupts.

For all DT-enabled boards, this call happens down in the
drivers/irqchip subsystem, after locating the target irqchip
driver from the device tree.

We still have a few instances of the boardfiles with machine
descriptors passing a machine-specific .handle_irq() to the
ARM kernel core.

Get rid of this by letting the few remaining machines consistently
call set_handle_irq() from the end of the .init_irq() callback
instead and diet down one member from the machine descriptor.

Cc: Marc Zyngier <maz@kernel.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>