ARM: imx: drop PL310 errata 588369 and 727915

The PL310 integrated on i.MX6 series and VF610 are revision r3p1 and
later.  Per ARM PL310 errata document, 588369 is fixed in r2p0 and
727915 is fixed in r3p1.  Neither is needed for i.MX6 or VF610.  So
let's drop them.

Signed-off-by: Shawn Guo <shawn.guo@freescale.com>