ramips: Rename POC registers

Rename POC registers.

The current code uses POC1-POC3.

The datasheet uses:
POC1: Port Control 0
POC1: Port Control 1
POC2: Port Control 2

So the first POC1 is a typo that should have been POC0, rename the
registers to POC0-POC2 accordingly.

Signed-off-by: Tobias Diedrich <ranma+openwrt@tdiedrich.de>

SVN-Revision: 33302