ARM: socfpga: make sure socfpga_cpu1start_addr is properly flushed

Make sure socfpga_cpu1start_addr is properly flushed from it's cache line so
that secondary cpu's can see it.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Tested-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
Signed-off-by: Dinh Nguyen <dinguyen@opensource.altera.com>