ARM i.MX25: Add missing clock gates

This completes the list of clock gates on the i.MX25. There are
several clocks marked as reserved in the datasheet, but nevertheless
used in the Freescale kernel. Add some comments to their positions
and add 'reservedx' entries to the clk enum. This way we can replace
them with the real names should we need them later. Adding the reserved
entry names will help us keeping the clk numbers when moving to devicetree.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>