omap: emif: deal with rams that return duplicate mr data on all byte lanes

Some rams (Micron for example) return duplicate mr data on all byte lanes.

Users of the get_mr function currently don't deal with this duplicated
data gracefully.  This patch detects the duplicated data and returns only
the expected 8 bit mr data.

Signed-off-by: Steve Sakoman <steve@sakoman.com>