ARMV7: OMAP3: Apply Cortex-A8 errata workarounds only on affected revisions

The workarounds for errata 621766 and 725233 should only be applied
on affected Cortex-A8 revisions.  Recent chips use r3px cores where
these have been fixed.

Signed-off-by: Mans Rullgard <mans@mansr.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>