ARM: 7715/1: MCPM: adapt to GIC changes after upstream merge

Since commit c0114709 ("irqchip: gic: Perform the gic_secondary_init()
call via CPU notifier") it is no longer required nor possible to call
gic_secondary_init() from platform code.

Signed-off-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>