Add OMAP3 architecture specific dcache flush back in.

Commit 78104ae isolates
the cache handling to appropriate handlers, but certain
architectures may need special handling esp during boot
time.
without this patch, building barebox with
	omap3530_beagle_per_uart_defconfig
and attempting to use peripheral download with pusb/pserial
will fail as OMAP ROM code depends on 2nd stage bootloaders
to clean up things.

Discussion Thread: http://www.spinics.net/lists/u-boot-v2/msg01286.html

Cc: Michael <mgr@pengutronix.de>
Cc: Sascha Hauer <s.hauer@pengutronix.de>

Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>