[ARM] pxa: removing dead XSCALE_CACHE_ERRATA

XSCALE_CACHE_ERRATA doesn't exist in Kconfig, therefore removing all
references for it from the source code.

Signed-off-by: Christoph Egger <siccegge@cs.fau.de>
Cc: Nicolas Pitre <nico@fluxnic.net>
Signed-off-by: Eric Miao <eric.y.miao@gmail.com>