UBUNTU: SAUCE: IMX51: only export NEON flag to userspace on Freescale iMX51 rev3.x or later silicon

BugLink: http://bugs.launchpad.net/bugs/507416

NEON function is broken on old Freescale iMX51 silicons, such as rev1.x and
rev2.x. Since more and more iMX51 based products will move to rev3.x or later
silicon, we need to enable NEON on these newer silicons and disable NEON on
those old ones.

This patch will detect the silicon revision dynamically and only export NEON
flag to userspace on Freescale iMX51 rev3.x or later silicon. It was tested on
Babbage 3.0 board and Babbage 2.x board.

Signed-off-by: Bryan Wu <bryan.wu@canonical.com>
Signed-off-by: Andy Whitcroft <apw@canonical.com>