ip17xx: The big rename

Recognize that the driver supports many more devices than the ip175c.

The driver itself is now called ip17xx, all generic functions have been
renamed to ip17xx_*. The model-dependent functions have prefixes ip175c_
and ip175d_.

Signed-off-by: Martin Mares <mj@ucw.cz>
Signed-off-by: Patrick Horn <patrick.horn@gmail.com>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@21723 3c298f89-4303-0410-b956-a3cf2f4a3e73