Add DT binding documentation for i.MXRT1050 clock driver.

Cc: Giulio Benetti <giulio.benetti@benettiengineering.com>
Signed-off-by: Jesse Taube <Mr.Bossman075@gmail.com>
Reviewed-by: Stephen Boyd <sboyd@kernel.org>
Link: https://lore.kernel.org/r/20220111215415.2075257-5-Mr.Bossman075@gmail.comSigned-off-by: Abel Vesa <abel.vesa@nxp.com>