[ARM] Kirkwood: invalidate L2 cache before enabling it

I get random oopses on my Kirkwood board at startup when L2 cache is
enabled. FYI I'm using Marvell uboot version 3.4.16

Each boot produces the same oops, but anything that changes the kernel
size (even only changing initramfs) makes the oops different.

I noticed that nothing invalidates the L2 cache before enabling it,
doing so fixes my problem.
Signed-off-by: NMaxime Bizon <mbizon@freebox.fr>
Signed-off-by: NNicolas Pitre <nico@marvell.com>

arch/arm/mm/cache-feroceon-l2.c

@@ -115,6 +115,10 @@ static inline void l2_inv_pa_range(unsigned long start, unsigned long end)
 	raw_local_irq_restore(flags);
 }
 
+static inline void l2_inv_all(void)
+{
+	__asm__("mcr p15, 1, %0, c15, c11, 0" : : "r" (0));
+}
 
 /*
  * Linux primitives.
@@ -321,6 +325,7 @@ static void __init enable_l2(void)
 
 		d = flush_and_disable_dcache();
 		i = invalidate_and_disable_icache();
+		l2_inv_all();
 		write_extra_features(u | 0x00400000);
 		if (i)
 			enable_icache();