flush I-cache after omap_sram_push()

This patch implements a suggestion by Richard Woodruff
<r-woodruff2@ti.com>.  omap_sram_push() copies executable code into
SRAM memory.  Currently this happens before Linux executes anything
from the SRAM, so we don't have to worry about evicting any SRAM lines
from the I-cache.  But at some point in the future, the SRAM might be
used more dynamically, adding and removing code while the system is
running.  So we should ensure that the I-cache is clean or at
least up-to-date after the copy.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Richard Woodruff <r-woodruff2@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>