ARM: dts: imx35: restore existing used clock enumeration

A new element got inserted into enum mx35_clks with commit 3713e3f5
("clk: imx35: define two clocks for rtc"). This insertion shifted most
nummerical clock assignments to a new nummerical value which in turn
rendered most hardcoded nummeric values in imx35.dtsi incorrect.

Restore the existing order by moving the newly introduced clock to the
end of the enum. Update the dts documentation accordingly.

Signed-off-by: Alexander Kurz <akurz@blala.de>
Fixes: 3713e3f5 ("clk: imx35: define two clocks for rtc")
Cc: <stable@vger.kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>