Revert "ARM: cache-l2x0: update workaround for PL310 errata 727915"

This reverts commit 8d4558d7721a3cb5c34c8931d3799d69b2b650f5.

Fixed upstream already:
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/arch/arm/mm/cache-l2x0.c?id=ab4d536890853ab6675ede65db40e2c0980cb0ea
ARM: 7398/1: l2x0: only write to debug registers on PL310

Picked up from here:
http://omapzoom.org/?p=kernel/omap.git;a=commit;h=5995fe0cda85b4160dffda6cbe2c6b5d7f44d7b6
3.13 rebase fixes

Change-Id: If6e378c71d967c1cab43a007a5223516f3898c89