ARM: 8483/1: Documentation: l2c: Rename l2cc to l2c2x0

ARM: 8483/1: Documentation: l2c: Rename l2cc to l2c2x0

The documentation in the l2cc.txt is specific to the L2 cache
controllers L2C210/L2C220/L2C310 (also known as PL210/PL220/PL310
and variants) and not generic as the file name implies. It's not
valid for integrated L2 controllers as found in e.g.
Cortex-A15/A7/A57/A53.

Reflect this by adapting the file name accordingly.

Signed-off-by: Dirk Behme <dirk.behme@gmail.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>