ARM: mvebu: move L2 cache initialization in init_early()

In preparation for moving the IRQ controller driver to
drivers/irqchip/, we don't want the IRQ controller driver to be
responsible for initializing the L2 cache. Instead, let's initialize
the L2 cache at the init_early() level, like mach-exynos/common.c is
doing.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Tested-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>