Add ARM errata workaround 852421 and 852423 for Cortex-A17

ARM errata 852421 and 852423 applies to r1p0, r1p1 and r1p2
revisions of Cortex-A17 processors. These workarounds
exist in Linux kernel and I thought it would be better
to add them in to U-Boot.

Signed-off-by: Nisal Menuka <nisalmenuka23@gmail.com>