[ARM] MX35: add clock support

This patch adds clock support for i.MX35 SoCs. We do not support setting
of clock rates yet, but most interesting clock rates should be reported.
I couldn't test all clock rates and the datasheet contains some obvious
bugs, so expect some bugs in this code.

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